vulnerability / NVI-00003875 / Revision 3
phpseclib has a variable-time HMAC comparison in SSH2::get_binary_packet() using != instead of hash_equals()
OSV carries this publisher advisory for phpseclib/phpseclib, phpseclib/phpseclib, phpseclib/phpseclib. This is an aggregated source copy; consult the original publisher and compare update dates.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
3.7 LOW (3.1)
security-advisories@github.com severity; no combined Null risk score.
0.361%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.29972. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
phpseclib/phpseclib
source listedECOSYSTEM: introduced 0.1.1; fixed 1.0.28
# 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
phpseclib/phpseclib
source listedECOSYSTEM: introduced 2.0.0; fixed 2.0.53
# 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
phpseclib/phpseclib
source listedECOSYSTEM: introduced 3.0.0; fixed 3.0.51
# 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
03 / Response
What to do next
- vendor patch
The original advisory lists fixed boundaries 1.0.28 for phpseclib/phpseclib. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- vendor patch
The original advisory lists fixed boundaries 2.0.53 for phpseclib/phpseclib. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- vendor patch
The original advisory lists fixed boundaries 3.0.51 for phpseclib/phpseclib. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-r854-jrxh-36qx ↗
GitHub Advisory Database via OSV · vendor advisory
Observed . GitHub-origin advisory, CC-BY-4.0; OSV is an aggregate copy, not independent corroboration.
- CVE-2026-40194 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-40194 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 2 ·
Source facts changed; compare the preserved prior revision.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.