GnuPG CVE-2026-57062

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. The CVSS AV:L metric indicates the malicious CMS content must be processed locally - while the crafted message can arrive via email or file transfer, gpgsm must be invoked against it on the local system. AC:H further constrains exploitation, requiring precise crafting of the CMS structure to manipulate the aes-ICVlen field to 4 bytes while maintaining a parseable envelope. No authentication on the target system is required per PR:N. Systems that do not use gpgsm, do not process S/MIME or CMS content, or do not accept CMS input from untrusted sources are not meaningfully exposed. The 'Information Disclosure' tag applied in source intelligence conflicts with the CVSS C:N metric; confidentiality impact is not confirmed by any available data and should not be assumed.

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. No EPSS data was provided in the available intelligence, so exploitation probability cannot be quantified numerically. The vulnerability is not listed in the CISA KEV catalog, and no public POC is referenced in the available data. The 'Information Disclosure' tag applied to this CVE appears inconsistent with the CVSS C:N metric - this discrepancy should be verified with the vendor, as the CVE description does not clearly support a confidentiality impact and may reflect erroneous tagging. The primary real-world risk is cryptographic: accepting a 4-byte authentication tag instead of 12 bytes drastically reduces the security margin of AES-GCM integrity verification from 2^96 to 2^32 combinations, potentially enabling forged or tampered CMS messages to pass verification. Despite this cryptographic concern, AV:L and AC:H substantially limit practical exploitability, making this a low operational priority unless the environment processes untrusted CMS/S/MIME content at scale.

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. No public POC has been identified; successful exploitation would require precise knowledge of CMS encoding structure and GnuPG's internal parsing behavior.