Incorrect cryptographic message parsing

Summary

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. By accepting an authentication tag length of 4 bytes instead of the required 12 bytes, this vulnerability allows for a low-impact data integrity issue where the cryptographic validity of messages could be compromised. A Low-impact flaw in GnuPG's gpgsm component accepts an incorrect AES-GCM authentication tag length in CMS messages. This compromises cryptographic data integrity, though confidentiality and availability are unaffected. Red Hat severity: Low — CVSS 2.9 (CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N). Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat Hardened Images. Will not fix / out of support: Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7. Red Hat does not currently list a fixing RHSA for this CVE.