The Common Vulnerabilities and Exposures (CVE) identifier CVE-2024-27316 refers to a memory exhaustion vulnerability found in the nghttp2 library, specifically when handling HTTP/2 incoming headers that exceed the limit. The vulnerability arises as the incoming headers are temporarily buffered in nghttp2 to generate an HTTP 413 (Payload Too Large) response. If a client does not stop sending headers, this leads to memory exhaustion. In this blog post, we will discuss the details of this vulnerability, including code snippets, links to original references, and exploit details.

Vulnerability Details (CVE-2024-27316)

HTTP/2 is a major revision of the HTTP protocol, bringing improvements like multiplexing, header compression, prioritization, and flow control over a single physical TCP connection. One of the requirements of the HTTP/2 protocol is that the server must restrict the maximum amount of headers a client can send when initiating a request.

The nghttp2 library is a popular implementation of the HTTP/2 protocol, both on the client and server-side. It provides essential features like support for HPACK header compression, flow control, etc. However, when handling incoming HTTP/2 headers that exceed the server-imposed limit, nghttp2 temporarily buffers these headers in order to generate a meaningful HTTP 413 (Payload Too Large) response.

When the client does not stop sending headers after receiving an HTTP 413 response, the temporary buffer storing the headers in nghttp2 can grow unchecked, ultimately leading to memory exhaustion.

Code Snippet

The following code snippet from nghttp2 demonstrates how incoming HTTP/2 headers are temporarily buffered in order to generate the HTTP 413 (Payload Too Large) response:

int nghttp2_submit_http413_response(nghttp2_session *session, int32_t stream_id, const nghttp2_nva *nva, size_t nvlen){
  nghttp2_data_provider data_prd;
  nghttp2_nv *nv;
  nghttp2_nv *nva_end;
  Error err;
  ...
  err = pack_headers(&bufs, &nva, &nva_end, session, stream_id, nva, nvlen);

  if(err != ){
    return err;
  }

  data_prd.read_callback = fixed_length_data_source_read_callback;
  nghttp2_submit_data(session, NGHTTP2_DATA_FLAG_EOF, stream_id, &data_prd);
}

Exploit Details

An attacker can exploit this vulnerability by crafting a request with an excessive number of HTTP/2 headers and continuously sending them to the target server. The attacker's goal is to cause a denial-of-service (DoS) attack by consuming all available memory resources on the target server. The attacker would typically bypass any network-level defenses by sending the headers at a slow rate to avoid triggering rate-limiting mechanisms.

References

1. Original nghttp2 GitHub Repository: [(https://github.com/nghttp2/nghttp2)]
2. HTTP/2 Specification (RFC 754): [(https://tools.ietf.org/html/rfc754)]
3. Mitre's Official CVE-2024-27316 Record: [(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-27316)]
4. Security Advisory for CVE-2024-27316 in the National Vulnerability Database (NVD): [(https://nvd.nist.gov/vuln/detail/CVE-2024-27316)]

Conclusion

CVE-2024-27316 is a critical vulnerability in the nghttp2 library, which can lead to memory exhaustion when HTTP/2 incoming headers exceed the limit. It is crucial to apply patches and updates provided by the library maintainers as soon as they become available to prevent any potential exploitation. Besides, monitoring ingress and egress traffic for unusual patterns can help prevent or mitigate potential attacks.

Timeline

Published on: 04/04/2024 20:15:08 UTC
Last modified on: 04/21/2024 04:15:08 UTC