EUVD-2026-38550
GHSA-m6x2-4hhh-669j
Severity by source
AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
CMS messages are delivered over network channels such as email (AV:N); crafting a valid malformed ICV requires expertise (AC:H); a user must trigger gpgsm processing (UI:R); no confidentiality impact is supported by the description.
Primary rating from Vendor (mitre).
CVSS VectorVendor: mitre
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Lifecycle Timeline
1DescriptionCVE.org
CMS (Cryptographic Message Syntax) parsing in gpgsm in GnuPG through 2.5.20 mishandles the CMS format for AES-GCM because aes-ICVlen is supposed to be 12 bytes but 4 bytes is accepted. NOTE: this is related to CVE-2026-34182.
AnalysisAI
GnuPG's gpgsm component through version 2.5.20 improperly validates AES-GCM authentication tag length during CMS parsing, accepting a 4-byte ICV where the cryptographic standard mandates 12 bytes. This validation failure means gpgsm will process CMS-formatted messages with a truncated integrity check value, undermining the authentication guarantee that AES-GCM is specifically designed to provide. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the target runs GnuPG through 2.5.20 and uses the gpgsm component to process externally-supplied CMS-formatted data containing AES-GCM encryption. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 base score of 2.9 (Low) with vector AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N places this at the lowest practical threat tier. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker crafts a malicious CMS-formatted message containing AES-GCM ciphertext with a deliberately shortened 4-byte ICV field rather than the required 12 bytes, then delivers it to a target who processes it with gpgsm (for example, via an S/MIME email). The parser accepts the truncated ICV without raising a validation error, potentially allowing forged or attacker-modified ciphertext to pass AES-GCM integrity verification undetected. … |
| Remediation | The primary remediation is to upgrade GnuPG to a version released after 2.5.20 that addresses this ICV length validation flaw; consult the official GnuPG download page at https://www.gnupg.org/download/ for the latest release, as no specific patched version number was confirmed in the available intelligence data. … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
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