phpseclib/phpseclib security advisory

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

CVE-2026-40194 is a low-severity user enumeration vulnerability in the PHP package phpseclib/phpseclib (CVSS 3.7), published 10 April 2026. It is fixed in 1.0.28, 2.0.53 and 3.0.51, one per release line; earlier versions on each line are affected. It can be exploited without an account.

low 3.7 published 2026-04-10 · updated 2026-06-17

Affected versions: >= 0.1.1, < 1.0.28
>= 2.0.0, < 2.0.53
>= 3.0.0, < 3.0.51
Fixed in: 1.0.28, 2.0.53, 3.0.51
Newest release: 4.0.3
Severity: Low · CVSS 3.7
Type: User enumeration
CWE-208
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Is your phpseclib/phpseclib version affected?

Run composer show phpseclib/phpseclib in your project, then enter the version. We check it against this and every other known phpseclib/phpseclib advisory.

Who can exploit CVE-2026-40194

Access: No account. Anyone who can send a request to an app that uses the affected code.
Conditions: It only works under specific conditions the attacker does not fully control (CVSS rates the attack as high complexity).

CVSS vector (scored by GitHub): CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Your app is only exposed if it uses the affected part of phpseclib/phpseclib. The advisory below says which part that is. If you are not sure, upgrade anyway: it costs less than finding out.

How to fix CVE-2026-40194 in phpseclib/phpseclib

Find the installed version: composer show phpseclib/phpseclib. If you never required it yourself, composer why phpseclib/phpseclib shows which package pulls it in.
Update it: composer update phpseclib/phpseclib --with-all-dependencies. You need the fixed version for your release line (1.0.28, 2.0.53 and 3.0.51).
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "phpseclib/phpseclib": "^3.0.51" if you can take that version), or upgrade the package that requires it.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-40194.
Commit composer.lock and deploy it. On the server, run composer install --no-dev from the lock file, not composer update.

If you cannot upgrade yet

General hardening for user enumeration issues while the upgrade waits. None of it replaces the fix.

Rate-limit login and password-reset endpoints and return the same response for unknown and known users.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-40194 advisory

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.

Description from the CVE record, published by GitHub (the CVE Numbering Authority), via the NVD entry for CVE-2026-40194. Advisory title: “phpseclib has a variable-time HMAC comparison in SSH2::get_binary_packet() using != instead of hash_equals()”.

References

GitHub advisory GHSA-r854-jrxh-36qx github.com
Fix commit ffe48b6 github.com
Release 1.0.28 github.com
Release 2.0.53 github.com
Release 3.0.51 github.com

Other phpseclib/phpseclib advisories

medium CVE-2026-84308: Phpseclib — non-constant-time X25519 scalar multiplication permits full private-key recovery 2026-09-08
medium CVE-2026-55599: Phpseclib: X.509 certificate validation sends attacker-controlled outbound requests (server-side request forgery) via Authority… 2026-06-16
high CVE-2026-44167: Phpseclib has a CVE-2024-27355 mitigation bypass — OID amplification DoS in ASN1::decodeOID() 2026-05-05
high CVE-2026-32935: Phpseclib's AES-CBC unpadding susceptible to padding oracle timing attack 2026-03-19
high CVE-2023-52892: Name confusion in x509 Subject Alternative Name fields 2024-06-28
high CVE-2024-27354: Phpseclib a large prime can cause a denial of service 2024-03-02

Need help patching or upgrading? Laskyr does PHP and Laravel security fixes and upgrades. Tell us what you run and we reply with a plan and a price.

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Where this data comes from

Affected and fixed versions: the Packagist security advisories API (GitHub Advisory Database and FriendsOfPHP), the same data composer audit uses. Synced 2026-11-03.
Description, score, weakness and references: NIST National Vulnerability Database (NVD), checked 2026-11-04. This product uses data from the NVD API but is not endorsed or certified by the NVD.
Exploited-in-the-wild status: the CISA Known Exploited Vulnerabilities catalog, checked 2026-11-04.
Compiled by Daniel Lasek at Laskyr from the sources above. The summary, “who can exploit it”, “how to fix it” and hardening sections are our plain-English reading of the record and are generated from it. The quoted description is the record's own text. Spot an error? Tell us.