CVE-2026-84308

MEDIUMPre-NVD 6.36.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 88% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Elevated
6.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.3Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

phpseclib is a PHP secure communications library. Prior to 3.0.57 and 4.0.1, pure-PHP X25519 scalar multiplication in phpseclib/Math/PrimeField/Integer.php performs data-dependent conditional modular reductions in add() and subtract(). During the Montgomery ladder in phpseclib/Crypt/EC/BaseCurves/Montgomery.php, the reduction behavior of each step depends on the secret scalar prefix, creating per-step timing and libgmp call-count observations that can reveal a reused 251-bit clamped private scalar. The phpseclib/Crypt/EC/Formats/Keys/MontgomeryPrivate.php derivation path invokes the pure-PHP multiplication without a native-engine check, while phpseclib/Crypt/EC/Formats/Keys/PKCS8.php reaches it when ext-sodium is unavailable. Exploitation requires a reused or long-lived X25519 private key, knowledge of the corresponding public key, execution of the pure-PHP path, and a local observer capable of resolving individual ladder steps or libgmp entry-point calls. Ephemeral X25519 keys, including phpseclib's normal SSH exchange path, are not affected. Recovery of the scalar permanently compromises operations that reuse that key. This issue is fixed in versions 3.0.57 and 4.0.1.

CVSS v3
6.3
EG Score
6.3(medium)
EG Risk
44(Track*)
EG Risk 44/100SSVC: Track*

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity63% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Watch closely — could escalate to Attend.
EPSS PROB
0%
EPSS %ILE
12%
KEV
Not listed

Published

September 1, 2026

Last Modified

September 9, 2026

Advisory Details (4)

Auto-updated Sep 1, 2026
🔬 Proof of concept available. Patch available. Sources: github, github_commit, github_release.
github_release Patch Available

4.0.1

Patch available: phpseclib/phpseclib 4.0.1

https://github.com/phpseclib/phpseclib/releases/tag/4.0.1
github_release Patch Available

3.0.57

Patch available: phpseclib/phpseclib 3.0.57

https://github.com/phpseclib/phpseclib/releases/tag/3.0.57
github_commit Patch Available

commit fb56bc5bb900 (phpseclib/phpseclib)

Patch available: phpseclib/phpseclib 3.0.57 (contains commit fb56bc5bb900)

https://github.com/phpseclib/phpseclib/commit/fb56bc5bb9009b54a6c26b31aeec8ed944f17373
github Patch Available🟡 PoC Available

phpseclib 3.0.56 — non-constant-time X25519 scalar multiplication permits full private-key recovery · Advisory · phpseclib/phpseclib · GitHub

https://github.com/phpseclib/phpseclib/security/advisories/GHSA-q97c-8qh3-fpc6

Vendor Advisories for CVE-2026-84308(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(5 across 4 ecosystems)
Debian:14(2)
PackageVulnerable rangeFixed inDependents
php-phpseclib33.0.43-2 ... 3.0.56-1 (16 versions)3.0.57-1—
php-phpseclib44.0.0-14.0.1-1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
php-phpseclib33.0.19-1 ... 3.0.57-1 (38 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
php-phpseclib33.0.43-2 ... 3.0.57-1 (19 versions)——
Packagist(1)
PackageVulnerable rangeFixed inDependents
phpseclib—4.0.1—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 12× in last 7d / 32× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-18 21:25 UTCEG score recompute
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-17 20:42 UTCEG score recompute
  4. 2026-09-17 19:32 UTCEPSS rescore
  5. 2026-09-16 18:39 UTCEG score recompute
  6. 2026-09-16 14:09 UTCEPSS rescore
  7. 2026-09-16 05:15 UTCEPSS rescore
  8. 2026-09-15 18:29 UTCEG score recompute
  9. 2026-09-15 03:12 UTCEPSS rescore
  10. 2026-09-15 03:12 UTCEPSS rescore
  11. 2026-09-13 19:23 UTCEG score recompute
  12. 2026-09-12 19:50 UTCEG score recompute
  13. 2026-09-11 20:17 UTCEG score recompute
  14. 2026-09-11 14:53 UTCEPSS rescore
  15. 2026-09-11 14:53 UTCEPSS rescore
  16. 2026-09-10 20:44 UTCEG score recompute
  17. 2026-09-08 23:22 UTCEG score recompute
  18. 2026-09-08 22:01 UTCEPSS rescore
  19. 2026-09-07 17:01 UTCEG score recompute
  20. 2026-09-06 17:28 UTCEG score recompute
  21. 2026-09-06 13:48 UTCEPSS rescore
  22. 2026-09-05 17:55 UTCEG score recompute
  23. 2026-09-05 15:31 UTCEPSS rescore
  24. 2026-09-04 18:21 UTCEG score recompute
  25. 2026-09-04 05:07 UTCEPSS rescore
Show 7 more
  1. 2026-09-03 18:45 UTCEG score recompute
  2. 2026-09-03 17:45 UTCEG score recompute
  3. 2026-09-02 20:00 UTCEG score recompute
  4. 2026-09-02 14:12 UTCEPSS rescore
  5. 2026-09-01 20:19 UTCEG score recompute
  6. 2026-09-01 19:35 UTCEG score recompute
  7. 2026-09-01 19:32 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-84308?
CVE-2026-84308 is a medium vulnerability published on September 1, 2026. phpseclib is a PHP secure communications library. Prior to 3.0.57 and 4.0.1, pure-PHP X25519 scalar multiplication in phpseclib/Math/PrimeField/Integer.php performs data-dependent conditional modular reductions in add() and subtract(). During the Montgomery ladder in…
When was CVE-2026-84308 disclosed?
CVE-2026-84308 was first published in the National Vulnerability Database on September 1, 2026, with the most recent update on September 9, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-84308 actively exploited?
CVE-2026-84308 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 88.2% of all scored CVEs.
What is the CVSS score of CVE-2026-84308?
CVE-2026-84308 has a CVSS v3 base score of 6.3 (NVD).
How do I remediate CVE-2026-84308?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-84308, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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