CVE-2026-40194 LOW

CVE-2026-40194: phpseclib has a variable-time HMAC comparison in SSH2::get_binary_packet() using != instead of hash_equals()

Vendor Phpseclib
Product phpseclib
Weakness CWE-208
Published April 10, 2026
Last update May 8, 2026
View on NVD All CVEs

CVSS base score

3.7/10
Attack vector Network
Attack complexity High
Privileges required None
User interaction None
Confidentiality Low
Integrity None

CVSS vector

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

What the vulnerability does

Description

phpseclib is a PHP secure communications library. Starting in 0.1.1 and prior to 3.0.51, 2.0.53, and 1.0.28, phpseclib\Net\SSH2::get_binary_packet() uses PHP's != operator to compare a received SSH packet HMAC against the locally computed HMAC. != on equal-length binary strings in PHP uses memcmp(), which short-circuits on the first differing byte. This is a real variable-time comparison (CWE-208), proven by scaling benchmarks. This vulnerability is fixed in 3.0.51, 2.0.53, and 1.0.28.

Key dates

Disclosure timeline

April 10, 2026 CVE published
May 8, 2026 Record updated