Bug 2494666 (CVE-2026-13758)

Summary: CVE-2026-13758 CryptX: CryptX for Perl: Message forgery via non-constant time AEAD tag comparison
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in CryptX for Perl. The library performs a non-constant time comparison of Authenticated Encryption with Associated Data (AEAD) authentication tags in its streaming decryption function. This timing difference creates a tag-verification oracle, allowing a remote attacker to submit multiple candidate tags and measure the timing. By exploiting this, an attacker can recover the expected tag byte by byte, leading to the forgery of messages that appear legitimate.
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Bug Depends On: 2494712, 2494713    
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Description OSIDB Bzimport 2026-06-29 21:02:27 UTC 
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.