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CVE-2026-84308— phpseclib — non-constant-time X25519 scalar multiplication permits full private-key recovery

Quick assessment

Affected
phpseclib phpseclib
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

phpseclib是phpseclib组织开源的一个提供加密算法与证书处理的库。 phpseclib 3.0.57之前版本和4.0.0至4.0.1之前版本存在侧信道信息泄露漏洞，该漏洞源于纯PHP X25519标量乘法中的数据依赖条件模约减，产生时序和libgmp调用计数差异，可能泄露复用的X25519私钥，导致使用该密钥的操作被永久破坏。

CVSS 6.3 · Medium EPSS 0.33% · P25

Affected Version Matrix 2

VendorProduct Version RangeStatus
phpseclib phpseclib < 3.0.57 affected
>= 4.0.0, < 4.0.1 affected
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I. Basic Information for CVE-2026-84308

Vulnerability Information
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Vulnerability Title
phpseclib — non-constant-time X25519 scalar multiplication permits full private-key recovery
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
通过时间差异性导致的信息暴露
Source: CVE Program / CVE List V5
Vulnerability Title
phpseclib 侧信道信息泄露漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
phpseclib是phpseclib组织开源的一个提供加密算法与证书处理的库。 phpseclib 3.0.57之前版本和4.0.0至4.0.1之前版本存在侧信道信息泄露漏洞，该漏洞源于纯PHP X25519标量乘法中的数据依赖条件模约减，产生时序和libgmp调用计数差异，可能泄露复用的X25519私钥，导致使用该密钥的操作被永久破坏。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
phpseclib phpseclib < 3.0.57 -

II. Public POCs for CVE-2026-84308

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III. Intelligence Information for CVE-2026-84308

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Patches & Fixes for CVE-2026-84308 (1)

Vendor Advisories for CVE-2026-84308 (1)

Vendor Pages for CVE-2026-84308 (2)

IV. Related Vulnerabilities

Same product: phpseclib
Same vendor: phpseclib
Same weakness: CWE-208

V. Comments for CVE-2026-84308

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