VulnerabilityDeferred

CVE-2026-13758

An attacker who can submit many candidate tags for the same nonce, ciphertext and associated data while measuring the timing precisely enough may recover the expected tag byte by byte and forge a message that verifies.

LOW 3.7EPSS 0.40%

Does this matter?

Lower severity and a low EPSS score (0.40%). Track it; it rarely justifies an emergency change on its own.

Description

CryptX versions before 0.088_001 for Perl compare AEAD authentication tags in non-constant time in the streaming decrypt_done path. The decrypt_done($tag) form compares it against the computed tag with memNE (memcmp() != 0), which short-circuits on the first differing byte, so its run time depends on the number of matching leading bytes. This affects all five AEAD modes: GCM, CCM, ChaCha20Poly1305, EAX and OCB. The one-shot *_decrypt_verify helpers are unaffected; they verify the tag inside libtomcrypt with a constant-time comparison. The timing difference is a tag-verification oracle. An attacker who can submit many candidate tags for the same nonce, ciphertext and associated data while measuring the timing precisely enough may recover the expected tag byte by byte and forge a message that verifies.

CVSS 3.1: 3.7 LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
EPSS: 0.40% probability · 33th percentile
CISA KEV: Not listed
Weakness: CWE-208
Source: 9b29abf9-4ab0-4765-b253-1875cd9b441e

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.