Vulnerability-Lookup

GHSA-R353-4845-PR5P

Vulnerability from github – Published: 2026-03-13 20:44 – Updated: 2026-03-16 22:01

Summary

simplesamlphp/xml-security: Missing AES-GCM Authentication Tag Validation on Encrypted Nodes Allows for Unauthorized Decryption

Details

Summary

XML nodes encrypted with either aes-128-gcm, aes-192-gcm, or aes-256-gcm lack validation of the authentication tag length. An attacker can use this to brute-force an authentication tag, recover the GHASH key, and decrypt the encrypted nodes. It also allows to forge arbitrary ciphertexts without knowing the encryption key.

Details

When decrypting with either aes-128-gcm, aes-192-gcm, or aes-256-gcm here, the $authTag is set from a substr(), but never has its length validated (it should be validated with something like strlen($authTag) == self::AUTHTAG_LENGTH). For that reason, a shorter than expected data blob will allow for the $authTag to have as short a tag as only one byte (see PHP's documentation).

See this example:

function test($data) {
    $ivSize = 12;
    $tagSize = 16;

    $iv = substr($data, 0, $ivSize);
    $data = substr($data, $ivSize);
    $offset = 0 - $tagSize;
    $tag = substr($data, $offset);
    $ct = substr($data, 0, $offset);

    echo 'IV: "' . $iv . '"' . PHP_EOL;
    echo 'Tag: "' . $tag . '"' . PHP_EOL;
    echo 'CT: "' . $ct . '"' . PHP_EOL;
}

/* Outputs:
php > test('myNonceNoncet');
IV: "myNonceNonce"
Tag: "t"
CT: ""
php > test('myNonceNonceta');
IV: "myNonceNonce"
Tag: "ta"
CT: ""
php > test('myNonceNoncetag');
IV: "myNonceNonce"
Tag: "tag"
CT: ""
*/

With a legit ciphertext in hand, this is enough to recover the GHASH key. With that key, any authenticated tags can be computed offline which allows for decryption of the ciphertext and forgery of arbitrary ciphertexts. PoC

Setup a server expecting XML with an encrypted assertion
Run this php script poc.php with php -S 127.0.0.1:8888 (taken from this saml test case)
The script expects this private key: sp-private-key.pem.
Create an XML document with an encrypted assertion (encrypted with aes-256-gcm)

Here is the SAMLResponse used in the video below: saml_response.txt

Note: The steps from 3 to 6 are implemented in this exploit script: nonce_reuse_with_fmt_val_oracle.py. You can run the script with sage -python nonce_reuse_with_fmt_val_oracle.py -s 'url-encoded_and_base64-encoded_samlresponse'

Take the content of the node and apply the following modifications
Base64-decode the content
Take the first 12 bytes and save them as the nonce
Take the last 16 bytes and save them as the tag
Now brute-force the tag of an empty ciphertext
Loop through all 256 possible byte values (let's call that byte_tag_attempt)
Concatenate together the nonce and the byte_tag_attempt
Base64-encode the result
Replace the content of the node with this result
On http errors 500, we learn that the tag is valid
Do the same for the next byte of the tag until all 16 bytes have been brute-forced
With this new tag and the empty ciphertext, compute the GHASH key (the way to do this has been described in this blog post)
Use this GHASH key to compute authentication tags offline for arbitrary ciphertexts
Decryption is done by observing XML parsing errors that occur after modifying the ciphertext, those can be seen as http errors 500

https://private-user-images.githubusercontent.com/20672053/531768743-2f6e4a7e-4384-4350-b423-7ddd77aa9152.webm?jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJnaXRodWIuY29tIiwiYXVkIjoicmF3LmdpdGh1YnVzZXJjb250ZW50LmNvbSIsImtleSI6ImtleTUiLCJleHAiOjE3NzMzMTQ3MjEsIm5iZiI6MTc3MzMxNDQyMSwicGF0aCI6Ii8yMDY3MjA1My81MzE3Njg3NDMtMmY2ZTRhN2UtNDM4NC00MzUwLWI0MjMtN2RkZDc3YWE5MTUyLndlYm0_WC1BbXotQWxnb3JpdGhtPUFXUzQtSE1BQy1TSEEyNTYmWC1BbXotQ3JlZGVudGlhbD1BS0lBVkNPRFlMU0E1M1BRSzRaQSUyRjIwMjYwMzEyJTJGdXMtZWFzdC0xJTJGczMlMkZhd3M0X3JlcXVlc3QmWC1BbXotRGF0ZT0yMDI2MDMxMlQxMTIwMjFaJlgtQW16LUV4cGlyZXM9MzAwJlgtQW16LVNpZ25hdHVyZT0zNDRhZThlYTY5OWNmNGZmMmNmOGJhYTNkNzAwMjNiMTVhMDMxOTIzMGRkN2Y3OGU3NTI3NmFkMWE2OTgwMDFhJlgtQW16LVNpZ25lZEhlYWRlcnM9aG9zdCJ9.X9UVe9qpwX1YQYo34WmUI84KA0a28FKd4SGy15GEVMU

Impact

The general impact is:

XML nodes encrypted with AES-GCM can be decrypted by observing parsing differences XML nodes encrypted with AES-GCM can be modified to decrypt to an arbitrary value The GCM internal GHASH key can be recovered

In cases where the encryption key is embedded in the XML and is encrypted with the Service Provider's public key (like often done with SAML), the last two items don't have a big impact. This is because:

With the Service Provider's public key, an arbitrary ciphertext can be created with a known symmetric key The symmetric keys are generated on the fly every time the IdP creates a new SAMLResponse

In any case, secrets that are embedded in the XML, whether coming from an IdP, or from another scheme, can be decrypted.

Important: If static symmetric keys are used, as the GHASH key could have leaked, you must rotate those keys.

References

For additional information on the issue, you can refer to this blog post about the OpenSSL issue and how it can be exploited.

Severity ?

8.2 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "simplesamlphp/xml-security"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "2.3.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "simplesamlphp/xml-security"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.13.9"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-32600"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-354"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-13T20:44:21Z",
    "nvd_published_at": "2026-03-16T14:19:38Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nXML nodes encrypted with either aes-128-gcm, aes-192-gcm, or aes-256-gcm lack validation of the authentication tag length.\nAn attacker can use this to brute-force an authentication tag, recover the [GHASH key](https://en.wikipedia.org/wiki/Galois/Counter_Mode#:~:text=%29%20is%20the-,hash%20key,-%2C%20a%20string%20of), and decrypt the encrypted nodes.\nIt also allows to forge arbitrary ciphertexts without knowing the encryption key.\n\n### Details\n\nWhen decrypting with either aes-128-gcm, aes-192-gcm, or aes-256-gcm [here](https://github.com/robrichards/xmlseclibs/blob/2bdfd742624d739dfadbd415f00181b4a77aaf07/src/XMLSecurityKey.php#L467-L479), the $authTag is set from a substr(), but never has its length validated (it should be validated with something like strlen($authTag) == self::AUTHTAG_LENGTH).\nFor that reason, a shorter than expected data blob will allow for the $authTag to have as short a tag as only one byte (see [PHP\u0027s documentation](https://www.php.net/manual/en/function.openssl-decrypt.php#:~:text=The%20length%20of%20the%20tag%20is%20not%20checked%20by%20the%20function.%20It%20is%20the%20caller%27s%20responsibility%20to%20ensure%20that%20the%20length%20of%20the%20tag%20matches%20the%20length%20of%20the%20tag%20retrieved%20when%20openssl_encrypt()%20has%20been%20called.%20Otherwise%20the%20decryption%20may%20succeed%20if%20the%20given%20tag%20only%20matches%20the%20start%20of%20the%20proper%20tag.)).\n\nSee this example:\n\n```php\nfunction test($data) {\n    $ivSize = 12;\n    $tagSize = 16;\n\n    $iv = substr($data, 0, $ivSize);\n    $data = substr($data, $ivSize);\n    $offset = 0 - $tagSize;\n    $tag = substr($data, $offset);\n    $ct = substr($data, 0, $offset);\n\n    echo \u0027IV: \"\u0027 . $iv . \u0027\"\u0027 . PHP_EOL;\n    echo \u0027Tag: \"\u0027 . $tag . \u0027\"\u0027 . PHP_EOL;\n    echo \u0027CT: \"\u0027 . $ct . \u0027\"\u0027 . PHP_EOL;\n}\n\n/* Outputs:\nphp \u003e test(\u0027myNonceNoncet\u0027);\nIV: \"myNonceNonce\"\nTag: \"t\"\nCT: \"\"\nphp \u003e test(\u0027myNonceNonceta\u0027);\nIV: \"myNonceNonce\"\nTag: \"ta\"\nCT: \"\"\nphp \u003e test(\u0027myNonceNoncetag\u0027);\nIV: \"myNonceNonce\"\nTag: \"tag\"\nCT: \"\"\n*/\n```\n\nWith a legit ciphertext in hand, this is enough to recover the [GHASH key](https://en.wikipedia.org/wiki/Galois/Counter_Mode#:~:text=%29%20is%20the-,hash%20key,-%2C%20a%20string%20of).\nWith that key, any authenticated tags can be computed offline which allows for decryption of the ciphertext and forgery of arbitrary ciphertexts.\nPoC\n\n1. Setup a server expecting XML with an encrypted assertion\n  -  Run this php script [poc.php](https://github.com/user-attachments/files/24426600/poc.php.txt) with php -S 127.0.0.1:8888 (taken from [this saml test case](https://github.com/robrichards/xmlseclibs/blob/69fd63080bc47a8d51bc101c30b7cb756862d1d6/tests/saml/saml-decrypt.phpt#L62))\n\n  - The script expects this private key: [sp-private-key.pem.](https://github.com/user-attachments/files/24426620/sp-private-key.pem.txt)\n\n2. Create an XML document with an encrypted assertion (encrypted with aes-256-gcm)\n\nHere is the SAMLResponse used in the video below: [saml_response.txt](https://github.com/user-attachments/files/24426638/saml_response.txt)\n\nNote: The steps from 3 to 6 are implemented in this exploit script: [nonce_reuse_with_fmt_val_oracle.py](https://github.com/user-attachments/files/24426645/nonce_reuse_with_fmt_val_oracle.py).\nYou can run the script with sage -python nonce_reuse_with_fmt_val_oracle.py -s \u0027url-encoded_and_base64-encoded_samlresponse\u0027\n\n3. Take the content of the \u003cxenc:CipherValue\u003e node and apply the following modifications\n\n- Base64-decode the content\n\n- Take the first 12 bytes and save them as the nonce\n\n- Take the last 16 bytes and save them as the tag\n\n- Now brute-force the tag of an empty ciphertext\n\n  - Loop through all 256 possible byte values (let\u0027s call that byte_tag_attempt)\n\n  - Concatenate together the nonce and the byte_tag_attempt\n\n  - Base64-encode the result\n\n  - Replace the content of the \u003cxenc:CipherValue\u003e node with this result\n\n  - On http errors 500, we learn that the tag is valid\n\n  - Do the same for the next byte of the tag until all 16 bytes have been brute-forced\n\n4. With this new tag and the empty ciphertext, compute the [GHASH key](https://en.wikipedia.org/wiki/Galois/Counter_Mode#:~:text=%29%20is%20the-,hash%20key,-%2C%20a%20string%20of) (the way to do this has been described in this [blog post](https://frereit.de/aes_gcm/))\n\n5. Use this [GHASH key](https://en.wikipedia.org/wiki/Galois/Counter_Mode#:~:text=%29%20is%20the-,hash%20key,-%2C%20a%20string%20of) to compute authentication tags offline for arbitrary ciphertexts\n\n6. Decryption is done by observing XML parsing errors that occur after modifying the ciphertext, those can be seen as http errors 500\n\nhttps://private-user-images.githubusercontent.com/20672053/531768743-2f6e4a7e-4384-4350-b423-7ddd77aa9152.webm?jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJnaXRodWIuY29tIiwiYXVkIjoicmF3LmdpdGh1YnVzZXJjb250ZW50LmNvbSIsImtleSI6ImtleTUiLCJleHAiOjE3NzMzMTQ3MjEsIm5iZiI6MTc3MzMxNDQyMSwicGF0aCI6Ii8yMDY3MjA1My81MzE3Njg3NDMtMmY2ZTRhN2UtNDM4NC00MzUwLWI0MjMtN2RkZDc3YWE5MTUyLndlYm0_WC1BbXotQWxnb3JpdGhtPUFXUzQtSE1BQy1TSEEyNTYmWC1BbXotQ3JlZGVudGlhbD1BS0lBVkNPRFlMU0E1M1BRSzRaQSUyRjIwMjYwMzEyJTJGdXMtZWFzdC0xJTJGczMlMkZhd3M0X3JlcXVlc3QmWC1BbXotRGF0ZT0yMDI2MDMxMlQxMTIwMjFaJlgtQW16LUV4cGlyZXM9MzAwJlgtQW16LVNpZ25hdHVyZT0zNDRhZThlYTY5OWNmNGZmMmNmOGJhYTNkNzAwMjNiMTVhMDMxOTIzMGRkN2Y3OGU3NTI3NmFkMWE2OTgwMDFhJlgtQW16LVNpZ25lZEhlYWRlcnM9aG9zdCJ9.X9UVe9qpwX1YQYo34WmUI84KA0a28FKd4SGy15GEVMU\n\n### Impact\n\nThe general impact is:\n\nXML nodes encrypted with AES-GCM can be decrypted by observing parsing differences\nXML nodes encrypted with AES-GCM can be modified to decrypt to an arbitrary value\nThe GCM internal [GHASH key](https://en.wikipedia.org/wiki/Galois/Counter_Mode#:~:text=%29%20is%20the-,hash%20key,-%2C%20a%20string%20of) can be recovered\n\nIn cases where the encryption key is embedded in the XML and is encrypted with the Service Provider\u0027s public key (like often done with SAML), the last two items don\u0027t have a big impact.\nThis is because:\n\nWith the Service Provider\u0027s public key, an arbitrary ciphertext can be created with a known symmetric key\nThe symmetric keys are generated on the fly every time the IdP creates a new SAMLResponse\n\nIn any case, secrets that are embedded in the XML, whether coming from an IdP, or from another scheme, can be decrypted.\n\nImportant: If static symmetric keys are used, as the [GHASH key](https://en.wikipedia.org/wiki/Galois/Counter_Mode#:~:text=%29%20is%20the-,hash%20key,-%2C%20a%20string%20of) could have leaked, you must rotate those keys.\n\n### References\nFor additional information on the issue, you can refer to this [blog post](https://sideni.xyz/posts/exploiting_openssl_api/) about the OpenSSL issue and how it can be exploited.",
  "id": "GHSA-r353-4845-pr5p",
  "modified": "2026-03-16T22:01:35Z",
  "published": "2026-03-13T20:44:21Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/simplesamlphp/xml-security/security/advisories/GHSA-r353-4845-pr5p"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-32600"
    },
    {
      "type": "WEB",
      "url": "https://github.com/simplesamlphp/xml-security/commit/cad6d57cf0a5a0b7e0cc4e4a5b18752e56eb1520"
    },
    {
      "type": "WEB",
      "url": "https://github.com/simplesamlphp/xml-security/commit/fdc12449e959c610943f9fd428e95e3832d74c25"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/simplesamlphp/xml-security"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "simplesamlphp/xml-security: Missing AES-GCM Authentication Tag Validation on Encrypted Nodes Allows for Unauthorized Decryption"
}

CVE-2026-32600 (GCVE-0-2026-32600)

Vulnerability from cvelistv5 – Published: 2026-03-13 19:58 – Updated: 2026-03-16 14:03

Title

xml-security is Missing AES-GCM Authentication Tag Validation on Encrypted Nodes Allows for Unauthorized Decryption

Summary

xml-security is a library that implements XML signatures and encryption. Prior to versions 2.3.1 and 1.13.9, XML nodes encrypted with either aes-128-gcm, aes-192-gcm, or aes-256-gcm lack validation of the authentication tag length. An attacker can use this to brute-force an authentication tag, recover the GHASH key, and decrypt the encrypted nodes. It also allows to forge arbitrary ciphertexts without knowing the encryption key. This vulnerability is fixed in 2.3.1 and 1.13.9.

Severity ?

8.2 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

CWE

CWE-354 - Improper Validation of Integrity Check Value

Assigner

GitHub_M

References

URL

Tags

	https://github.com/simplesamlphp/xml-security/sec…	x_refsource_CONFIRM
	https://github.com/simplesamlphp/xml-security/com…	x_refsource_MISC
	https://github.com/simplesamlphp/xml-security/com…	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	simplesamlphp	xml-security	Affected: >= 2.0.0, < 2.3.1 Affected: < 1.13.9

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-32600",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-03-16T14:01:30.383537Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-03-16T14:03:17.811Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "xml-security",
          "vendor": "simplesamlphp",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.0.0, \u003c 2.3.1"
            },
            {
              "status": "affected",
              "version": "\u003c 1.13.9"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "xml-security is a library that implements XML signatures and encryption. Prior to versions 2.3.1 and 1.13.9, XML nodes encrypted with either aes-128-gcm, aes-192-gcm, or aes-256-gcm lack validation of the authentication tag length. An attacker can use this to brute-force an authentication tag, recover the GHASH key, and decrypt the encrypted nodes. It also allows to forge arbitrary ciphertexts without knowing the encryption key. This vulnerability is fixed in 2.3.1 and 1.13.9."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 8.2,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "LOW",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-354",
              "description": "CWE-354: Improper Validation of Integrity Check Value",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-03-16T12:28:57.720Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/simplesamlphp/xml-security/security/advisories/GHSA-r353-4845-pr5p",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/simplesamlphp/xml-security/security/advisories/GHSA-r353-4845-pr5p"
        },
        {
          "name": "https://github.com/simplesamlphp/xml-security/commit/cad6d57cf0a5a0b7e0cc4e4a5b18752e56eb1520",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/simplesamlphp/xml-security/commit/cad6d57cf0a5a0b7e0cc4e4a5b18752e56eb1520"
        },
        {
          "name": "https://github.com/simplesamlphp/xml-security/commit/fdc12449e959c610943f9fd428e95e3832d74c25",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/simplesamlphp/xml-security/commit/fdc12449e959c610943f9fd428e95e3832d74c25"
        }
      ],
      "source": {
        "advisory": "GHSA-r353-4845-pr5p",
        "discovery": "UNKNOWN"
      },
      "title": "xml-security is Missing AES-GCM Authentication Tag Validation on Encrypted Nodes Allows for Unauthorized Decryption"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-32600",
    "datePublished": "2026-03-13T19:58:41.692Z",
    "dateReserved": "2026-03-12T14:54:24.269Z",
    "dateUpdated": "2026-03-16T14:03:17.811Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-R353-4845-PR5P

Summary

Details

Impact

References

CVE-2026-32600 (GCVE-0-2026-32600)

Tags

Sightings

Nomenclature