CVE-2026-40194CWE-208

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

Low · published April 10, 2026

CVSS v3.1
3.7
EPSS
0%
Percentile
29.3
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
3.7 · LOW
Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
CVSS v4.0
Not supplied
EPSS
0.00367 · 29.3th percentile
Weakness
CWE-208 · Observable Timing Discrepancy
Published
2026-04-10T20:24Z
EPSS history
Timeline
  • 10 APR 20:24Z
    phpseclib has a variable-time HMAC comparison in SSH2::get_binary_packet() using != instead of hash_equals()
    cvelistv5