JEDI-SEC | Security Research & Digital Defense

GHSA-h6cr-wjv9-3cpp: Forge: Denial of Service via infinite loop in BigInteger.modInverse() with negative input (incomplete fix of CVE-2026-33891)

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  • Severity: LOW
  • CVE: CVE-2026-118781
  • Ecosystems: npm
  • Packages: node-forge

### Summary

`BigInteger.prototype.modInverse()` in node-forge’s bundled jsbn library enters an infinite loop when the value or the modulus is negative, for example when a negative public exponent is passed to `forge.pki.rsa.generateKeyPair()`. This is an incomplete fix of CVE-2026-33891 (GHSA-5m6q-g25r-mvwx), which handled only a zero value. Fixed in node-forge 1.4.1.

### Details

`bnModInverse()` (`lib/jsbn.js`, exposed as `forge.jsbn.BigInteger.prototype.modInverse`) implements the binary extended Euclidean algorithm (Handbook of Applied Cryptography, Algorithm 14.61), which is defined for positive integers. With a negative operand the loop cannot terminate: `rShiftTo` is an arithmetic shift, so a negative value never moves towards zero, and the loop’s exit condition (`u` reaching zero) is never met. The calling thread spins at 100% CPU indefinitely; in Node.js this blocks the event loop. Memory does not grow.

node-forge 1.4.0 fixed CVE-2026-33891 (GHSA-5m6q-g25r-mvwx) by returning zero early when `this.signum() == 0`, although its changelog describes the check as “

Source: GitHub Security Advisories · 2026-10-30

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