chore: pin JWT validation parameters

README.md

@@ -186,7 +186,7 @@ Configure environment variables in `wrangler.toml` under `[vars]`, or set them v
 * **`ATTACHMENT_TOTAL_LIMIT_KB`** (Optional): 
   - Max total attachment storage per user in KB. 
   - Example: `1048576` for 1GB.
-* **`ATTACHMENT_TTL_SECS`** (Optional, Default: `300`): 
+* **`ATTACHMENT_TTL_SECS`** (Optional, Default: `300`, Minimum: `60`): 
   - TTL for attachment upload/download URLs.
 
 ### Scheduled Tasks (Cron)

src/attachments.js

@@ -9,6 +9,8 @@
  * Route matching and URL parsing should be handled by `src/entry.js`.
  */
 
+const JWT_EXPECTED_ALG = "HS256";
+const JWT_VALIDATION_LEEWAY_SECS = 60;
 // JWT validation using Web Crypto API (no external dependencies)
 async function verifyJwt(token, secret) {
   const encoder = new TextEncoder();
@@ -19,6 +21,17 @@ async function verifyJwt(token, secret) {
 
   const [headerB64, payloadB64, signatureB64] = parts;
 
+  let header;
+  try {
+    header = JSON.parse(new TextDecoder().decode(base64UrlDecode(headerB64)));
+  } catch {
+    throw new Error("Invalid token header");
+  }
+
+  if (!header || typeof header !== "object" || header.alg !== JWT_EXPECTED_ALG) {
+    throw new Error("Invalid token algorithm");
+  }
+
   // Import the secret key for HMAC-SHA256
   const key = await crypto.subtle.importKey(
     "raw",
@@ -40,12 +53,23 @@ async function verifyJwt(token, secret) {
   }
 
   // Decode and parse the payload
-  const payload = JSON.parse(
-    new TextDecoder().decode(base64UrlDecode(payloadB64))
-  );
+  let payload;
+  try {
+    payload = JSON.parse(new TextDecoder().decode(base64UrlDecode(payloadB64)));
+  } catch {
+    throw new Error("Invalid token payload");
+  }
 
-  // Check expiration
-  if (payload.exp && payload.exp < Math.floor(Date.now() / 1000)) {
+  if (!payload || typeof payload !== "object") {
+    throw new Error("Invalid token payload");
+  }
+  
+  if (typeof payload.exp !== "number") {
+    throw new Error("Invalid token exp");
+  }
+  
+  const now = Math.floor(Date.now() / 1000);
+  if (payload.exp < now - JWT_VALIDATION_LEEWAY_SECS) {
     throw new Error("Token expired");
   }
 
@@ -442,5 +466,3 @@ export async function handleDownload(request, env, cipherId, attachmentId, token
     headers,
   });
 }
-
-

src/auth.rs

@@ -3,14 +3,17 @@ use axum::{
     http::{header, request::Parts},
 };
 use constant_time_eq::constant_time_eq;
-use jsonwebtoken::{decode, DecodingKey, Validation};
+use jsonwebtoken::{decode, Algorithm, DecodingKey, Validation};
 use serde::{Deserialize, Serialize};
+use std::collections::HashSet;
 use std::sync::Arc;
 use worker::Env;
 
 use crate::db;
 use crate::error::AppError;
 
+pub(crate) const JWT_VALIDATION_LEEWAY_SECS: u64 = 60;
+
 #[derive(Debug, Serialize, Deserialize)]
 pub struct Claims {
     pub sub: String,    // User ID
@@ -25,6 +28,19 @@ pub struct Claims {
     pub amr: Vec<String>,
 }
 
+pub(crate) fn jwt_validation() -> Validation {
+    let mut required_spec_claims = HashSet::new();
+    required_spec_claims.insert("exp".to_string());
+
+    let mut validation = Validation::new(Algorithm::HS256);
+    validation.required_spec_claims = required_spec_claims;
+    validation.leeway = JWT_VALIDATION_LEEWAY_SECS;
+    validation.validate_exp = true;
+    validation.validate_nbf = true;
+    validation.algorithms = vec![Algorithm::HS256];
+    validation
+}
+
 /// AuthUser extractor - provides (user_id, email) tuple
 pub struct AuthUser(
     pub String, // user_id
@@ -55,7 +71,7 @@ impl FromRequestParts<Arc<Env>> for Claims {
 
         // Decode and validate the token
         let decoding_key = DecodingKey::from_secret(secret.to_string().as_ref());
-        let token_data = decode::<Claims>(&token, &decoding_key, &Validation::default())
+        let token_data = decode::<Claims>(&token, &decoding_key, &jwt_validation())
             .map_err(|_| AppError::Unauthorized("Invalid token".to_string()))?;
 
         let claims = token_data.claims;

src/handlers/attachments.rs

@@ -14,7 +14,7 @@ use uuid::Uuid;
 use worker::{query, wasm_bindgen::JsValue, Bucket, D1Database, Env, HttpMetadata};
 
 use crate::{
-    auth::Claims,
+    auth::{Claims, JWT_VALIDATION_LEEWAY_SECS},
     db,
     error::AppError,
     models::{
@@ -560,7 +560,7 @@ fn download_url(
     attachment_id: &str,
     user_id: &str,
 ) -> Result<String, AppError> {
-    let token = build_download_token(env, user_id, cipher_id, attachment_id)?;
+    let token = build_upload_download_token(env, user_id, cipher_id, attachment_id)?;
     let normalized_base = base_url.trim_end_matches('/');
     Ok(format!(
         "{normalized_base}/api/ciphers/{cipher_id}/attachment/{attachment_id}/download?token={token}"
@@ -734,7 +734,7 @@ fn validate_size_within_declared(
     Ok(())
 }
 
-fn build_download_token(
+fn build_upload_download_token(
     env: &Env,
     user_id: &str,
     cipher_id: &str,
@@ -744,6 +744,7 @@ fn build_download_token(
     let now = Utc::now().timestamp();
     let exp = now
         .checked_add(ttl_secs)
+        .and_then(|exp| exp.checked_sub(JWT_VALIDATION_LEEWAY_SECS as i64))
         .ok_or_else(|| AppError::Internal)?;
 
     if exp < 0 {
@@ -778,7 +779,7 @@ fn upload_url(
     attachment_id: &str,
     user_id: &str,
 ) -> Result<String, AppError> {
-    let token = build_download_token(env, user_id, cipher_id, attachment_id)?;
+    let token = build_upload_download_token(env, user_id, cipher_id, attachment_id)?;
     let normalized_base = base_url.trim_end_matches('/');
     Ok(format!(
         "{normalized_base}/api/ciphers/{cipher_id}/attachment/{attachment_id}/azure-upload?token={token}"

src/handlers/identity.rs

@@ -1,14 +1,14 @@
 use axum::{extract::State, Form, Json};
 use chrono::{Duration, Utc};
 use constant_time_eq::constant_time_eq;
-use jsonwebtoken::{decode, encode, DecodingKey, EncodingKey, Header, Validation};
+use jsonwebtoken::{decode, encode, DecodingKey, EncodingKey, Header};
 use serde::{Deserialize, Deserializer, Serialize};
 use serde_json::Value;
 use std::sync::Arc;
 use worker::{query, Env};
 
 use crate::{
-    auth::Claims,
+    auth::{jwt_validation, Claims},
     crypto::{ct_eq, generate_salt, hash_password_for_storage, validate_totp},
     db,
     error::AppError,
@@ -494,7 +494,7 @@ pub async fn token(
             let token_data = decode::<RefreshClaims>(
                 &refresh_token,
                 &DecodingKey::from_secret(jwt_refresh_secret.as_ref()),
-                &Validation::default(),
+                &jwt_validation(),
             )
             .map_err(|_| AppError::Unauthorized("Invalid refresh token".to_string()))?;