Executive brief
CryptX is a security library for the Perl programming language used to encrypt and protect data. A flaw in how it verifies security 'tags' during decryption allows an attacker to potentially guess the correct tag by measuring tiny differences in how long the computer takes to process different inputs. If successful, an attacker could bypass security checks and forge encrypted messages, though this requires a high degree of precision and many attempts.
Technical details
A timing side-channel exists in the `decrypt_done()` method across all five AEAD modes (GCM, CCM, ChaCha20Poly1305, EAX, and OCB). The vulnerability is caused by the use of `memNE` (a non-constant time memory comparison) to verify authentication tags, which short-circuits upon encountering the first differing byte. This creates a tag-verification oracle where the execution time depends on the number of matching leading bytes. An attacker capable of making precise timing measurements over a network or local interface could iteratively recover the expected authentication tag and forge valid ciphertexts. The issue is fixed in version 0.088_001 by implementing constant-time comparison. One-shot decryption helpers were not affected as they utilize libtomcrypt's internal constant-time verification.
Affected products
- MIK CryptX before 0.088_001
Timeline
- 2026-04-23: patched: Version 0.088_001 released with security fixes.
- 2026-06-29: disclosed: CVE-2026-13758 published.