CVE-2026-13758

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 v3.1 Score

3.7

LOW

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS — Exploit Prediction

0.0030

Probability of exploitation

0.21%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-208 CWE-208

References

Other References

https://github.com/DCIT/perl-CryptX/commit/7e56347d420aaf43b2ee1586f4a230492ccf1642.patch https://metacpan.org/release/MIK/CryptX-0.088_001/changes http://www.openwall.com/lists/oss-security/2026/06/29/19

Frequently Asked Questions

What is CVE-2026-13758? +

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. It has a CVSS v3.1 base score of 3.7 (LOW).

How severe is CVE-2026-13758? +

CVE-2026-13758 has a CVSS v3.1 score of 3.7 out of 10, rated LOW. This is a low-severity vulnerability with limited impact. The EPSS score is 0.0030, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-13758? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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