OESA-2026-3004 (CVE-2026-42766)
Vulnerability from osv_openeuler – Published: 2026-07-19 11:11 – Updated: 2026-08-06 11:11 – Source websiteEDK II is a modern, feature-rich, cross-platform firmware development environment for the UEFI and PI specifications.
Security Fix(es):
Issue summary: A specially crafted password-encrypted CMS message can trigger a NULL pointer dereference during CMS decryption.
Impact summary: This NULL pointer dereference leads to an application crash and a Denial of Service.
The CMS PasswordRecipientInfo.keyDerivationAlgorithm field is defined as OPTIONAL in the ASN.1 specification and may therefore be absent in specially crafted inputs. During the password-based CMS decryption the OpenSSL CMS implementation dereferences this field without first checking whether it was present.
An attacker who supplies such a CMS message to an application performing password-based CMS decryption can trigger an application crash, leading to a Denial of Service.
Applications that process password-encrypted CMS messages may be affected.
The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.(CVE-2026-42766)
Issue summary: The CMS_decrypt and PKCS7_decrypt functions are vulnerable to Bleichenbacher-style attack when an attacker is able to provide the CMS or S/MIME messages and observe the error code and/or decryption output.
Impact summary: The Bleichenbacher-style attack allows an attacker to use the victim's vulnerable application as a way to decrypt or sign messages with the victim's private RSA key.
The attack is possible in 2 variants.
- The decryption API (CMS_decrypt(), PKCS7_decrypt()) is used without providing the recipient certificate. In this case OpenSSL iterates over every KeyTransRecipientInfo (KTRI) without stopping at the first success.
An attacker who authors a message with two KTRI entries — the first one wrapping a real CEK under the victim's public key, the second with an arbitrary probe ciphertext — obtains opportunity to iterate the 2nd KTRI to get a valid PKCS#1 v1.5 padding if the error code of the application is available.
That is a Bleichenbacher oracle (Bleichenbacher, CRYPTO '98): an adaptive-chosen-ciphertext side channel from which the attacker decrypts any RSA ciphertext to the victim's key or forges any PKCS#1 v1.5 signature under it.
- When the decryption API (CMS_decrypt(), PKCS7_decrypt()) is provided with the recipient certificate, and the recipient is not found, a random key is substituted.
An attacker who authors a message and is able to compare both error code and the result of the decryption, can mount a Bleichenbacher oracle.
We are not aware of any applications that provide a remote attacker an opportunity to mount an attack described in these scenarios. We consider the existence of such application very unlikely, and for this reason this CVE has been evaluated as Low severity.
To avoid these attacks, when RSA PKCS#1 v1.5 Key Transport is in use, the invoked EVP_PKEY_decrypt() will use the implicit rejection mechanism described in draft-irtf-cfrg-rsa-guidance. In previous OpenSSL releases the implicit rejection was explicitly disabled.
The implicit rejection mechanism always returns a plaintext value, the symmetric key. This result is deterministic for the ciphertext and the private key. The length of the decryption result can happen to match the length of the key of the symmetric cipher that was used for the content encryption. When a certificate is not provided, the last RecipientInfo producing a key that looks valid will be used. It may cause getting garbage content on decryption. As a proper way to deal with this a recipient certificate has to be provided to identify the particular RecipientInfo for decryption.
The FIPS modules in 4.0, 3.6, 3.5, and 3.4 are not affected by this issue, as CMS and S/MIME processing happens outside the OpenSSL FIPS module boundary.(CVE-2026-42768)
| URL | Type | |
|---|---|---|
{
"affected": [
{
"ecosystem_specific": {
"aarch64": [
"edk2-debuginfo-202002-38.oe2003sp4.aarch64.rpm",
"edk2-debugsource-202002-38.oe2003sp4.aarch64.rpm",
"edk2-devel-202002-38.oe2003sp4.aarch64.rpm"
],
"noarch": [
"edk2-aarch64-202002-38.oe2003sp4.noarch.rpm",
"edk2-help-202002-38.oe2003sp4.noarch.rpm",
"edk2-ovmf-202002-38.oe2003sp4.noarch.rpm",
"python3-edk2-devel-202002-38.oe2003sp4.noarch.rpm"
],
"src": [
"edk2-202002-38.oe2003sp4.src.rpm"
],
"x86_64": [
"edk2-debuginfo-202002-38.oe2003sp4.x86_64.rpm",
"edk2-debugsource-202002-38.oe2003sp4.x86_64.rpm",
"edk2-devel-202002-38.oe2003sp4.x86_64.rpm"
]
},
"package": {
"ecosystem": "openEuler:20.03-LTS-SP4",
"name": "edk2",
"purl": "pkg:rpm/openEuler/edk2\u0026distro=openEuler-20.03-LTS-SP4"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "202002-38.oe2003sp4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"database_specific": {
"severity": "Medium"
},
"details": "EDK II is a modern, feature-rich, cross-platform firmware development environment for the UEFI and PI specifications.\r\n\r\nSecurity Fix(es):\n\nIssue summary: A specially crafted password-encrypted CMS message\ncan trigger a NULL pointer dereference during CMS decryption.\n\nImpact summary: This NULL pointer dereference leads to an application crash\nand a Denial of Service.\n\nThe CMS PasswordRecipientInfo.keyDerivationAlgorithm field is defined as\nOPTIONAL in the ASN.1 specification and may therefore be absent in specially\ncrafted inputs. During the password-based CMS decryption the OpenSSL\nCMS implementation dereferences this field without first checking whether it\nwas present.\n\nAn attacker who supplies such a CMS message to an application performing\npassword-based CMS decryption can trigger an application crash, leading to\na Denial of Service.\n\nApplications that process password-encrypted CMS messages may be affected.\n\nThe FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this\nissue, as the affected code is outside the OpenSSL FIPS module boundary.(CVE-2026-42766)\n\nIssue summary: The CMS_decrypt and PKCS7_decrypt functions are vulnerable to\nBleichenbacher-style attack when an attacker is able to provide the CMS or\nS/MIME messages and observe the error code and/or decryption output.\n\nImpact summary: The Bleichenbacher-style attack allows an attacker to use the\nvictim\u0026apos;s vulnerable application as a way to decrypt or sign messages with the\nvictim\u0026apos;s private RSA key.\n\nThe attack is possible in 2 variants.\n\n1. The decryption API (CMS_decrypt(), PKCS7_decrypt()) is used without\nproviding the recipient certificate. In this case OpenSSL iterates over every\nKeyTransRecipientInfo (KTRI) without stopping at the first success.\n\nAn attacker who authors a message with two KTRI entries \u2014 the first one\nwrapping a real CEK under the victim\u0026apos;s public key, the second with an\narbitrary probe ciphertext \u2014 obtains opportunity to iterate the 2nd KTRI to\nget a valid PKCS#1 v1.5 padding if the error code of the application is\navailable.\n\nThat is a Bleichenbacher oracle (Bleichenbacher, CRYPTO \u0026apos;98): an\nadaptive-chosen-ciphertext side channel from which the attacker decrypts any\nRSA ciphertext to the victim\u0026apos;s key or forges any PKCS#1 v1.5 signature under\nit.\n\n2. When the decryption API (CMS_decrypt(), PKCS7_decrypt()) is provided with\nthe recipient certificate, and the recipient is not found, a random\nkey is substituted.\n\nAn attacker who authors a message and is able to compare both error code and\nthe result of the decryption, can mount a Bleichenbacher oracle.\n\nWe are not aware of any applications that provide a remote attacker\nan opportunity to mount an attack described in these scenarios. We consider\nthe existence of such application very unlikely, and for this reason this\nCVE has been evaluated as Low severity.\n\nTo avoid these attacks, when RSA PKCS#1 v1.5 Key Transport is in use, the\ninvoked EVP_PKEY_decrypt() will use the implicit rejection mechanism described\nin draft-irtf-cfrg-rsa-guidance. In previous OpenSSL releases the implicit\nrejection was explicitly disabled.\n\nThe implicit rejection mechanism always returns a plaintext value,\nthe symmetric key. This result is deterministic for the ciphertext and the\nprivate key. The length of the decryption result can happen to match the\nlength of the key of the symmetric cipher that was used for the content\nencryption. When a certificate is not provided, the last RecipientInfo\nproducing a key that looks valid will be used. It may cause getting garbage\ncontent on decryption. As a proper way to deal with this a recipient\ncertificate has to be provided to identify the particular RecipientInfo for\ndecryption.\n\nThe FIPS modules in 4.0, 3.6, 3.5, and 3.4 are not affected by this issue, as\nCMS and S/MIME processing happens outside the OpenSSL FIPS module boundary.(CVE-2026-42768)",
"id": "OESA-2026-3004",
"modified": "2026-08-06T11:11:54Z",
"published": "2026-07-19T11:11:54Z",
"references": [
{
"type": "ADVISORY",
"url": "https://www.openeuler.org/zh/security/security-bulletins/detail/?id=openEuler-SA-2026-3004"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42766"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42768"
}
],
"schema_version": "1.7.2",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
],
"summary": "edk2 security update",
"upstream": [
"CVE-2026-42766",
"CVE-2026-42768"
]
}
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