Vulnerability in phpseclib/phpseclib (CVE-2026-40194)
Summary
Vulnerability in phpseclib/phpseclib (CVE-2026-40194). Risk of unauthorized operations or information disclosure. Exploitable via e819a163c. Mitigation: upgrade to 1.0.28 or later.
Original description
The description as published by the source.
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):
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_check…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-40194 has been found in phpseclib/phpseclib.
Attackers can target a specific entry point like e819a163c over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 3.7/10.
What to do: upgrade phpseclib/phpseclib to 1.0.28 or later.
If unsure, ask your IT team or search "phpseclib/phpseclib CVE-2026-40194" on the vendor's site.
CVE-2026-40194 (phpseclib/phpseclib) — CWE-208 / CVSS v3 3.7
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: e819a163c / master / memcmp / arcfour
Patched: 1.0.28 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-208) exists in phpseclib/phpseclib. Attackers reach the vulnerable code path via e819a163c without authentication.
Check the vendor advisory for the affected versions of phpseclib/phpseclib. Attack surface: e819a163c / master / memcmp / arcfour.
Severity: Low (CVSS 3.7/10). Risk of unauthorized operations or information disclosure.
Update to 1.0.28.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'phpseclib/phpseclib' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'phpseclib/phpseclib' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
phpseclib/phpseclibを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade phpseclib/phpseclib to 1.0.28ステージング環境で 1.0.28 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-40194 php-phpseclib
- Ubuntu UBUNTU-CVE-2026-40194 php-phpseclib Fixed in: 2.0.1-1ubuntu0.1~esm1
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com