Overview
CVE-2026-33746 describes a broken authentication scenario in Convoy where the JWT validation path failed to cryptographically verify the token signature. Specifically, the JWTService::decode() function validated only time-based claims (exp, nbf, iat) and did not enforce the SignedWith constraint, allowing an attacker to forge or tamper with the payload (for example, user_uuid) while the token would still be considered valid as long as the time-based claims were satisfied. This directly undermines SSO flows (LoginController::authorizeToken) and enables impersonation of arbitrary users, which is a severe authentication bypass. The issue was patched in version 4.5.1. While the CVE references a Convoy/kvm management context (and lcobucci/jwt in that ecosystem), the underlying vulnerability pattern translates to Go (Gin) services that neglect proper JWT signature verification, enabling similar token-forgery attacks if signature verification is bypassed or omitted in Go implementations.
In Go (Gin) contexts, typical missteps mirror the same root cause: code paths that parse tokens without validating the cryptographic signature or that rely solely on non-signature-based claims (such as exp) for authentication. A malicious actor can craft a valid-looking JWT with a forged user_id or user_uuid and reuse it to access privileged endpoints if the server does not verify the token’s signature against the intended secret/public key, or if it uses an unsafe parsing path (for example, parsing without verification). This not only defeats authentication but also undermines trust in the entire authorization workflow, enabling lateral movement and access to sensitive resources.
Remediation requires implementing robust JWT verification in Go with explicit signature validation, strict algorithm checks, and comprehensive claims validation. The fix mirrors best practices: parse tokens with a verification step that uses a known secret or public key, enforce the expected signing method, verify token.Valid, and validate critical claims (iss, aud, exp, nbf, iat) with a small clock skew. Additionally, rotate keys, add tests that cover valid and tampered tokens, and ensure the deployment uses patched libraries (as CVE-2026-33746 does in its patched release). The Go code example below shows vulnerable and fixed patterns side-by-side to illustrate the concrete remediation for Go (Gin).
Affected Versions
3.9.0-beta to 4.5.0
Code Fix Example
Go (Gin) API Security Remediation
package main
import (
"errors"
"fmt"
"net/http"
"os"
"time"
"github.com/gin-gonic/gin"
"github.com/golang-jwt/jwt/v4"
)
// Vulnerable: token parsing without signature verification
func extractUserIDVulnerable(tokenString string) (string, error) {
// Parse token without verifying the signature
token, _, err := new(jwt.Parser).ParseUnverified(tokenString, jwt.MapClaims{})
if err != nil {
return "", err
}
claims, ok := token.Claims.(jwt.MapClaims)
if !ok {
return "", fmt.Errorf("invalid claims")
}
// Rely solely on time-based claims (exp) without validating the signature
if exp, ok := claims["exp"].(float64); ok {
if int64(exp) < time.Now().Unix() {
return "", errors.New("token expired")
}
}
uid, _ := claims["user_id"].(string)
return uid, nil
}
// Fixed: verify signature and signing method
func extractUserIDFixed(tokenString string, secret string) (string, error) {
token, err := jwt.Parse(tokenString, func(t *jwt.Token) (interface{}, error) {
// Enforce a specific signing method (HMAC in this example)
if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
return nil, fmt.Errorf("unexpected signing method: %v", t.Header["alg"])
}
return []byte(secret), nil
})
if err != nil {
return "", err
}
if claims, ok := token.Claims.(jwt.MapClaims); ok && token.Valid {
uid, _ := claims["user_id"].(string)
return uid, nil
}
return "", fmt.Errorf("invalid token")
}
func main() {
r := gin.Default()
r.GET("/vulnerable", func(c *gin.Context) {
token := c.GetHeader("X-Token")
uid, err := extractUserIDVulnerable(token)
if err != nil {
c.JSON(http.StatusUnauthorized, gin.H{"error": err.Error()})
return
}
c.JSON(http.StatusOK, gin.H{"user_id": uid})
})
r.GET("/secure", func(c *gin.Context) {
token := c.GetHeader("X-Token")
uid, err := extractUserIDFixed(token, os.Getenv("JWT_SECRET"))
if err != nil {
c.JSON(http.StatusUnauthorized, gin.H{"error": err.Error()})
return
}
c.JSON(http.StatusOK, gin.H{"user_id": uid})
})
_ = r.Run(":8080")
}