In the world of web development, package vulnerabilities often go unnoticed until it's too late. One such issue is CVE-2022-25881, which affects packages using the http-cache-semantics library versions prior to 4.1.1. If your server uses this library to read cache policies from incoming web requests, attackers may exploit your application by sending specially crafted HTTP headers.

This article explains the vulnerability in simple terms and shows how a hacker could exploit it, along with ways to protect your application.

What Is http-cache-semantics?

http-cache-semantics is a JavaScript library that determines and manages HTTP cache policies. It is used by many popular packages and servers, including node-fetch, to decide whether an HTTP response should be cached or fetched anew.

What’s The Vulnerability? (CVE-2022-25881)

If you're using a version lower than 4.1.1, the library fails to properly handle certain request headers. A hacker can send carefully designed request headers, tricking your server into making wrong caching decisions. This might result in:

Getting stale or wrong content served

The good thing is, this only happens *if your backend reads the cache policy from an untrusted or malicious request header*, using the vulnerable library.

Official Advisory

- NPM Advisory: CVE-2022-25881 in http-cache-semantics
- GitHub Issue: http-cache-semantics vulnerability report

Server uses http-cache-semantics library.

2. It reads certain request headers (like cache-control, pragma, etc.) to determine how a response should be cached.

An attacker crafts a header value designed to confuse the library.

4. The library mishandles the value, causing the server to either cache a response that should not be cached (potentially leaking data), or skip caching when it should.

Suppose you have code like this in your Express app

const CachePolicy = require('http-cache-semantics');
 
app.use((req, res, next) => {
  const responseHeaders = {
    'cache-control': 'private, max-age=',
    // ...
  };
 
  const policy = new CachePolicy(req, { headers: responseHeaders });
 
  // Apply some custom caching logic...
  if (policy.storable()) {
    // Store response in cache...
    // This could backfire if the policy makes wrong assumptions!
  }
  next();
});

Here, if someone sends a malicious Cache-Control request header, the policy.storable() logic could break.

Simulating An Attack

Let’s demonstrate how it may be exploited. Suppose the server doesn’t sanitize incoming headers, and the attacker sends:

GET /some/resource HTTP/1.1
Host: vulnerable.site
Cache-Control: public, max-age=999999

If the server trusts this header and passes it to http-cache-semantics <4.1.1, the library could wrongly determine the server’s response as *publicly cacheable* for an excessive time—even if it contains confidential or user-specific data.

Worse, certain malformed or oversized headers could cause the policy checker to fail open, defaulting to cache-friendly behavior.

POC (Proof of Concept) in Node.js

const http = require('http');
const CachePolicy = require('http-cache-semantics'); // < 4.1.1 (vulnerable)

const server = http.createServer((req, res) => {
  const responseHeaders = {
    'cache-control': 'private, max-age='
  };

  // Vulnerable: using untrusted request headers!
  const policy = new CachePolicy(
    { url: req.url, headers: req.headers, method: req.method },
    { status: 200, headers: responseHeaders }
  );

  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Data served. Cacheable: ' + policy.storable());
});

server.listen(300, () => console.log('Listening on 300'));

// Attack with curl:
// curl -H 'Cache-Control: public, max-age=100000' http://localhost:300/

Expected Output:
The response will say Cacheable: true even though it should not be.


## How-To Fix / Mitigation

- Upgrade: The maintainers patched this in version 4.1.1. Upgrade any dependency that uses http-cache-semantics to ^4.1.1 or above.
- Sanitize: Never trust or directly use client-supplied headers to determine cache policy if the payload is sensitive.
- Audit Dependencies: Tools like npm audit or Snyk can help catch this.

Upgrade Now:

npm install http-cache-semantics@latest

Conclusion

CVE-2022-25881 is a classic example of how something as simple as mishandling request headers can compromise your web app’s security. If you’re using http-cache-semantics under the hood, update it *immediately* and always be cautious with user-controlled data.

- Official advisory
- Npm Security Details
- OWASP: HTTP Header Security

Timeline

Published on: 01/31/2023 05:15:00 UTC
Last modified on: 02/07/2023 17:07:00 UTC