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

### 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 "<= 0". Negative values were not covered, and a negative modulus was never handled. Every negative input that did terminate already returned zero. Within node-forge, RSA key generation is the only path to a negative operand: the caller's public exponent `e` becomes `BigInteger.fromInt(e)`, and `state.e.modInverse(state.phi)` is called with it. `gcd()` works on absolute values, so the coprimality checks pass and the loop is reached. Any exponent other than 3 or 65537 uses the pure JavaScript implementation, even when `forge.options.usePureJavaScript` is not set. RFC 8017, Section 3.1 requires the RSA public exponent to be at least 3. Values that node-forge parses (DER, PEM, JWK, PKCS#12, X.509, TLS) are always read as unsigned integers and cannot produce a negative operand. The fix makes `modInverse()` return zero when the value or the modulus is zero or negative, as it already does when no inverse