EUVD-2026-69576Severity by source
AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
Local timing observer required with co-tenancy; multiple non-default conditions must align (key reuse, pure-PHP path); private-key recovery enables both confidentiality and integrity violations.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
5DescriptionCVE.org
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.
AnalysisAI
Timing side-channel exposure in phpseclib's pure-PHP X25519 scalar multiplication allows a local observer to recover a reused 251-bit clamped private key. Data-dependent conditional modular reductions in PrimeField/Integer.php cause per-step timing and libgmp call-count variation during the Montgomery ladder, leaking scalar bits when the same private key is used across multiple operations. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires four simultaneous conditions to be present. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS base score of 6.3 (AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N) accurately reflects the constrained exploitation requirements, and the C:H/I:H impact metrics should not be read in isolation. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | The primary fix is upgrading to phpseclib 3.0.57 (3.x branch) or 4.0.1 (4.x branch), both confirmed available at the GitHub tagged releases. … Detailed patch versions, workarounds, and compensating controls in full report. |
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View allSame technique Information Disclosure
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External POC / Exploit Code
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