Vulnerability-Lookup

GHSA-XM5M-WGH2-RRG3

Vulnerability from github – Published: 2026-04-14 01:01 – Updated: 2026-04-14 01:01

Summary

Sigstore Timestamp Authority has Improper Certificate Validation in verifier

Details

Authorization bypass via certificate bag manipulation in sigstore/timestamp-authority verifier

An authorization bypass vulnerability exists in sigstore/timestamp-authority verifier (timestamp-authority/v2/pkg/verification): VerifyTimestampResponse function correctly verifies the certificate chain but when the TSA specific constraints are verified in VerifyLeafCert, the first non-CA certificate from the PKCS#7 certificate bag is used instead of the leaf certificate from the certificate chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key. The library validates the signature using the one certificate but performs authorization checks on the another, allowing an attacker to bypass some authorization controls.

This vulnerability does not apply to timestamp-authority service, only to users of timestamp-authority/v2/pkg/verification package.

This vulnerability does not apply to sigstore-go even though it is a user of timestamp-authority/v2/pkg/verification: Providing TSACertificate option to VerifyTimestampResponse fully mitigates the issue.

Patches

The issue will be fixed in timestamp-authority 2.0.6

Workarounds

Users of VerifyTimestampResponse can use the TSACertificate option to specify the exact certificate they expect to be used: this fully mitigates the issue.

References

This issue was found after reading CVE-2026-33753 / GHSA-3xxc-pwj6-jgrj (originally reported by @Jaynornj and @Pr00fOf3xpl0it)

Severity ?

5.5 (Medium)


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

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JSON

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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.0.5"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/sigstore/timestamp-authority/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.0.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-39984"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-295"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-14T01:01:59Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Authorization bypass via certificate bag manipulation in sigstore/timestamp-authority verifier\n\nAn authorization bypass vulnerability exists in sigstore/timestamp-authority verifier (timestamp-authority/v2/pkg/verification): `VerifyTimestampResponse` function correctly verifies the certificate chain but when the TSA specific constraints are verified in `VerifyLeafCert`, the first non-CA certificate from the PKCS#7 certificate bag is used instead of the leaf certificate from the certificate chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key. The library validates the signature using the one certificate but performs authorization checks on the another, allowing an attacker to bypass some authorization controls. \n\nThis vulnerability does **not** apply to timestamp-authority service, only to users of `timestamp-authority/v2/pkg/verification` package.\n\nThis vulnerability does **not** apply to sigstore-go even though it is a user of `timestamp-authority/v2/pkg/verification`: Providing `TSACertificate` option to  `VerifyTimestampResponse` fully mitigates the issue.\n\n\n### Patches\n\nThe issue will be fixed in timestamp-authority 2.0.6\n\n### Workarounds\n\nUsers of `VerifyTimestampResponse` can use the `TSACertificate` option to specify the exact certificate they expect to be used: this fully mitigates the issue.\n\n### References\n\nThis issue was found after reading CVE-2026-33753 / GHSA-3xxc-pwj6-jgrj (originally reported by @Jaynornj and @Pr00fOf3xpl0it)",
  "id": "GHSA-xm5m-wgh2-rrg3",
  "modified": "2026-04-14T01:01:59Z",
  "published": "2026-04-14T01:01:59Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sigstore/timestamp-authority/security/advisories/GHSA-xm5m-wgh2-rrg3"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/sigstore/timestamp-authority"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Sigstore Timestamp Authority has Improper Certificate Validation in verifier"
}

CVE-2026-39984 (GCVE-0-2026-39984)

Vulnerability from cvelistv5 – Published: 2026-04-14 23:41 – Updated: 2026-04-16 14:00

Title

Sigstore Timestamp Authority has Improper Certificate Validation in verifier

Summary

Sigstore Timestamp Authority is a service for issuing RFC 3161 timestamps. Versions 2.0.5 and below contain an authorization bypass vulnerability in the VerifyTimestampResponse function. VerifyTimestampResponse correctly verifies the certificate chain signature, but the TSA-specific constraint checks in VerifyLeafCert uses the first non-CA certificate from the PKCS#7 certificate bag instead of the leaf certificate from the verified chain. An attacker can exploit this by prepending a forged certificate to the certificate bag while the message is signed with an authorized key, causing the library to validate the signature against one certificate but perform authorization checks against another. This vulnerability only affects users of the timestamp-authority/v2/pkg/verification package and does not affect the timestamp-authority service itself or sigstore-go. The issue has been fixed in version 2.0.6.

Severity ?

5.5 (Medium)


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

CWE

CWE-295 - Improper Certificate Validation

Assigner

GitHub_M

References

URL

Tags

	https://github.com/sigstore/timestamp-authority/s…	x_refsource_CONFIRM
	https://github.com/sigstore/timestamp-authority/r…	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	sigstore	timestamp-authority	Affected: < 2.0.6

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-39984",
                "options": [
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                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-04-16T14:00:42.548200Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
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          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "timestamp-authority",
          "vendor": "sigstore",
          "versions": [
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        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "NONE",
            "baseScore": 5.5,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N",
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      "references": [
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          "url": "https://github.com/sigstore/timestamp-authority/security/advisories/GHSA-xm5m-wgh2-rrg3"
        },
        {
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    "datePublished": "2026-04-14T23:41:47.909Z",
    "dateReserved": "2026-04-08T00:01:47.628Z",
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    "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-XM5M-WGH2-RRG3

Authorization bypass via certificate bag manipulation in sigstore/timestamp-authority verifier

Patches

Workarounds

References

CVE-2026-39984 (GCVE-0-2026-39984)

Tags

Sightings

Nomenclature