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.

Affected: Packagist: phpseclib/phpseclib

# phpseclib SSH2: Variable-time comparison in HMAC verification

## Summary

`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.

The finding is **Low severity (defense-in-depth)**, not Critical. Practical exploitation over the network is prevented by SSH's disconnect-on-MAC-failure behavior combined with per-connection session keys. The fix is a one-liner: replace `!=` with `hash_equals()`, which the codebase already uses in 9 other places.

- **Target:** `phpseclib/phpseclib` - **File:** `phpseclib/Net/SSH2.php` - **Lines (master `e819a163c`):** 3405 and 3410 - **CWE:** CWE-208 (Observable Timing Discrepancy) - **CVSS v3.1:** 3.7 — `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N` - **Severity:** Low (cryptographic hygiene / defense-in-depth) - **Affected branches:** `master`, `3.0`, `2.0`, `1.0` (all supported versions)

## Root cause

`phpseclib/Net/SSH2.php` lines 3399-3415 (master at `e819a163c`):

```php if ($this->hmac_check instanceof Hash) { $reconstructed = !$this->hmac_check_etm ? pack('Na*', $packet->packet_length, $packet->plain) : substr($packet->raw, 0, -$this->hmac_size); if (($this->hmac_check->getHash() & "\xFF\xFF\xFF\xFF") == 'umac') { $this->hmac_chec…

Affected: Ubuntu:Pro:16.04:LTS: php-phpseclib, Ubuntu:Pro:16.04:LTS: phpseclib, Ubuntu:Pro:18.04:LTS: php-phpseclib, Ubuntu:Pro:18.04:LTS: phpseclib, Ubuntu:Pro:20.04:LTS: php-phpseclib, Ubuntu:Pro:20.04:LTS: phpseclib, Ubuntu:Pro:22.04:LTS: php-phpseclib, Ubuntu:Pro:22.04:LTS: php-phpseclib3, Ubuntu:Pro:22.04:LTS: phpseclib, Ubuntu:24.04:LTS: php-phpseclib3 and 8 more

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.

Ein Angreifer kann mehrere Schwachstellen in Cacti ausnutzen, um beliebigen Programmcode auszuführen, um Sicherheitsvorkehrungen zu umgehen, um einen Cross-Site Scripting Angriff durchzuführen, um einen SQL-Injection Angriff durchzuführen, um Dateien zu manipulieren, und um Informationen offenzulegen.