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fix: resolve JWT authentication bypass vulnerability (#1854) #1865

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fix: resolve JWT authentication bypass vulnerability (#1854) #1865

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3 changes: 2 additions & 1 deletion backend/config.js
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Original file line number Diff line number Diff line change
Expand Up @@ -7,13 +7,14 @@ const envSchema = z.object({
SUPABASE_URL: z.string().url().optional(),
SUPABASE_SERVICE_ROLE_KEY: z.string().optional(),
SUPABASE_ANON_KEY: z.string().optional(),
SUPABASE_JWT_SECRET: z.string().min(1, "SUPABASE_JWT_SECRET is required for JWT verification").optional(),
OPENROUTER_API_KEY: z.string().min(1),
PASSWORD_RESET_BASE_URL: z.string().url().optional(),
FRONTEND_URL: z.string().url().optional(),
CLIENT_URL: z.string().url().optional(),
EMAIL_USER: z.string().optional(),
EMAIL_PASS: z.string().optional(),
SITE_URL: z.string().url().optional(),
SITE_URL: z.string().optional(),
});

const _env = envSchema.safeParse(process.env);
Expand Down
55 changes: 36 additions & 19 deletions backend/middlewares/requireAuth.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,8 @@ import crypto from "crypto";
import { HttpError } from "../utils/httpError.js";
import { getSupabaseAdmin } from "../utils/supabase.js";

const ALLOWED_ALGORITHMS = ["HS256"];

const base64UrlDecode = (str) => {
str = str.replace(/-/g, "+").replace(/_/g, "/");
while (str.length % 4) {
Expand All @@ -10,6 +12,14 @@ const base64UrlDecode = (str) => {
return Buffer.from(str, "base64").toString("utf-8");
};

const constantTimeCompare = (a, b) => {
if (typeof a !== "string" || typeof b !== "string") return false;
if (a.length !== b.length) return false;
const bufA = Buffer.from(a);
const bufB = Buffer.from(b);
return crypto.timingSafeEqual(bufA, bufB);
};

const verifyLocalJwt = (token, secret) => {
try {
const parts = token.split(".");
Expand All @@ -18,13 +28,15 @@ const verifyLocalJwt = (token, secret) => {
const [headerB64, payloadB64, signatureB64] = parts;

const header = JSON.parse(base64UrlDecode(headerB64));

// Prevent algorithm confusion: Only process HS256 tokens using HMAC.
if (header.alg !== "HS256") {

if (!header || typeof header.alg !== "string") {
return null;
}

// Additional check: if the secret appears to be a PEM-encoded public key, reject HMAC

if (!ALLOWED_ALGORITHMS.includes(header.alg)) {
return null;
}

if (secret.startsWith("-----BEGIN")) {
return null;
}
Expand All @@ -37,19 +49,27 @@ const verifyLocalJwt = (token, secret) => {
.replace(/\//g, "_")
.replace(/=/g, "");

const expectedSignatureBuffer = Buffer.from(expectedSignature);
const signatureBuffer = Buffer.from(signatureB64);

if (
expectedSignatureBuffer.length !== signatureBuffer.length ||
!crypto.timingSafeEqual(expectedSignatureBuffer, signatureBuffer)
) {
if (!constantTimeCompare(expectedSignature, signatureB64)) {
return null;
}

const payload = JSON.parse(base64UrlDecode(payloadB64));

if (payload.exp && Date.now() >= payload.exp * 1000) {
const now = Math.floor(Date.now() / 1000);

if (typeof payload.exp === "number" && now >= payload.exp) {
return null;
}

if (typeof payload.iat === "number" && now < payload.iat) {
return null;
}

if (payload.iss && payload.iss !== "supabase") {
return null;
}

if (payload.aud && !Array.isArray(payload.aud) && typeof payload.aud !== "string") {
return null;
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}

Expand All @@ -71,7 +91,6 @@ if (!jwtSecret && isProduction) {
process.exit(1);
}

// Rate limiter specifically for the slow fallback path
const FALLBACK_WINDOW_MS = 60_000;
const FALLBACK_MAX_REQUESTS = 10;
const fallbackRateCounts = new Map();
Expand Down Expand Up @@ -120,7 +139,6 @@ export const requireAuth = async (req, res, next) => {
}

if (jwtSecret) {
// LOCAL HMAC verification - no network call
const payload = verifyLocalJwt(token, jwtSecret);
if (!payload) {
next(new HttpError(401, "Invalid or expired session"));
Expand All @@ -132,14 +150,13 @@ export const requireAuth = async (req, res, next) => {
email: payload.email,
user_metadata: payload.user_metadata,
app_metadata: payload.app_metadata,
role: payload.role
role: payload.role,
};
return next();
}

// DEVELOPMENT ONLY FALLBACK
console.warn("[security] Using slow network fallback for JWT verification. Do not use in production.");

const clientIp = req.socket?.remoteAddress || req.ip || "unknown";
if (isFallbackRateLimited(clientIp)) {
next(new HttpError(429, "Too many verification requests. Please try again later."));
Expand All @@ -154,7 +171,7 @@ export const requireAuth = async (req, res, next) => {
}

const { data: { user }, error } = await supabaseAdmin.auth.getUser(token);

if (error || !user) {
next(new HttpError(401, "Invalid or expired session"));
return;
Expand Down