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Maniphest T7900

Cleartext Signature Forgery in GnuPG
Testing, NormalPublic
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Description

[ Note that this is also the parent ticket for a couple of other reports by the same source]

In GnuPG implementation, g10/armor.c, the function parse_hash_header has an argument LINE and not have length of line.

When the header line input has is something like (expressed by C-escape for the NULL byte):

Hash: SHA256\x00....

The string after the NULL byte is ignored and it won't included in the computation of the signature.

This could be abused by an attacker and a user would see the string as if it's covered by the signature.

Reported-by: 49016 and Liam (two-heart)

Details

External Link
https://gnupg.org/blog/20251226-cleartext-signatures.html

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Event Timeline

• gniibe created this task.Nov 4 2025, 6:07 AM
• gniibe shifted this object from the S1 Public space to the Restricted Space space.
• gniibe changed the visibility from "Public (No Login Required)" to "g10code (Project)".
• gniibe changed the edit policy from "All Users" to "g10code (Project)".
• gniibe mentioned this in Unknown Object (Maniphest Task).Nov 10 2025, 2:51 AM
• werner closed subtask T7905: Radix64 Line-Truncation Enabling Polyglot Attacks as Resolved.Nov 11 2025, 9:53 AM
• werner updated the task description. (Show Details)Nov 14 2025, 1:27 PM
• werner changed the status of subtask T7906: Memory Corruption in ASCII-Armor Parsing from Open to Testing.Nov 19 2025, 5:38 PM
• werner changed the status of subtask T7908: GnuPG Accepts Path Separators and Path Traversals in Literal Data "Filename" Field from Open to Testing.Nov 19 2025, 5:43 PM
• werner updated the task description. (Show Details)Nov 19 2025, 5:49 PM
• werner changed the status of subtask T7904: GnuPG may downgrade digest algorithm to SHA1 from Open to Testing.Nov 19 2025, 5:53 PM
• gniibe changed the status of subtask T7909: Other bugs reported by 49016 et al. from Open to Testing.Nov 20 2025, 6:33 AM
• werner shifted this object from the Restricted Space space to the S1 Public space.Fri, Dec 26, 2:52 PM
• werner changed the visibility from "g10code (Project)" to "All Users".
• werner removed a project: g10code.
• werner added a subscriber: • werner.

Regarding the cleartext signature please see this piece: https://gnupg.org/blog/20251226-cleartext-signatures.html

thesamesam added a subscriber: thesamesam.Fri, Dec 26, 8:40 PM
• werner triaged this task as Normal priority.Mon, Dec 29, 4:54 PM
• werner edited projects, added OpenBSD, Not A Bug; removed Bug Report.
• werner changed the status of subtask T7901: Cleartext Signature Forgery in NotDashEscaped header implementation in GnuPG from Open to Testing.Mon, Dec 29, 7:13 PM
• werner closed subtask T7906: Memory Corruption in ASCII-Armor Parsing as Resolved.Tue, Dec 30, 9:56 AM
• werner changed the status of subtask T7907: Encrypted Message Malleability Checks are Incorrectly Enforced Causing Plaintext Recovery Attacks from Open to Testing.Fri, Jan 2, 4:22 PM
• werner closed subtask T7903: Multiple Plaintext Attack on Detached PGP Signatures in GnuPG as Resolved.Fri, Jan 2, 4:24 PM
• werner changed the status of subtask T7902: OpenPGP Cleartext Signature Framework from Open to Testing.Fri, Jan 2, 4:35 PM
• werner changed the task status from Open to Testing.Fri, Jan 2, 4:37 PM

(Testing for now for better visibility. Real or Semi-real bugs with fixes are already set to Resolved)

• werner changed the visibility from "All Users" to "Public (No Login Required)".Mon, Jan 5, 11:26 AM
• werner closed subtask T7904: GnuPG may downgrade digest algorithm to SHA1 as Resolved.Fri, Jan 9, 11:01 AM
pl13 mentioned this in Unknown Object (Maniphest Task).Mon, Jan 12, 9:31 AM
• werner set External Link to https://gnupg.org/blog/20251226-cleartext-signatures.html.Thu, Jan 15, 4:05 PM