CVE-2024-3302 - Unlimited HTTP/2 CONTINUATION frames leading to Browser Out of Memory Condition and Potential DoS Attack

The recent vulnerability identified as CVE-2024-3302 has been reported to affect Firefox < 125, Firefox ESR < 115.10, and Thunderbird < 115.10. This blog post will provide an in-depth analysis of the vulnerability, explore the potential risks, and give recommendations on how to mitigate the issue.

Vulnerability Details

CVE-2024-3302 is caused by an oversight in the implementation of the HTTP/2 protocol, specifically the processing of CONTINUATION frames. As per the HTTP/2 specifications, CONTINUATION frames are used to continue a sequence of header block fragments (a sequence of HEADER or PUSH_PROMISE frames followed by one or more CONTINUATION frames). However, it was discovered that there was no imposed limit on the number of CONTINUATION frames that could be processed by the affected browsers.

A malicious server can exploit this vulnerability by sending an excessive number of CONTINUATION frames to the client, leading to an Out of Memory (OOM) condition in the browser. This can potentially result in the browser crashing or a Denial of Service (DoS) attack which impacts the user's ability to access web content.

Below is a code snippet showcasing the issue in the redacted_client_processing.c file

void process_continuation_frames(redact_client_ctx *client) {
    redact_header_block_fragment *fragment = client->active_header_block_fragment;
    
    while (client->stream_has_more_data) {
        process_next_frame(client);
        if (client->frame.type != CONTINUATION) {
            // Handle error
            return;
        }
        // Append CONTINUATION frame payload to header block fragment
        fragment = append_continuation_payload(client, fragment);
    }
}

Notice that there is no limit on the number of times the process_next_frame function is called within the while loop. This means that a server can continue sending CONTINUATION frames indefinitely, causing the browser to allocate more and more memory for the received data.

Original References

- CVE-2024-3302 - MITRE's Official CVE Entry
- Mozilla Security Advisory - Official Advisory from Mozilla
- HTTP/2 RFC 754 - Official HTTP/2 Specification

Exploit Details

An attacker would be able to exploit this vulnerability by creating a malicious server (or compromising an existing server) that sends an excessive number of CONTINUATION frames to a victim's browser. Once a user visits the webpage hosted on the malicious server, the server can start sending these frames, causing the OOM condition in the browser to occur.

While no publicly known exploits for this vulnerability are available as of now, it is crucial to apply patches and update the affected browsers as soon as possible to minimize the risks.

Mitigation and Recommendations

The best way to mitigate this vulnerability is to update the affected software to the latest versions, as the patch for the CVE-2024-3302 vulnerability has been included in Firefox version 125, Firefox ESR version 115.10, and Thunderbird version 115.10. Users are strongly advised to update their browsers as soon as possible to protect against this vulnerability.

In conclusion, the CVE-2024-3302 vulnerability exposes users to potential OOM conditions and DoS attacks. Keeping your software up-to-date plays a critical role in securing browsers against such vulnerabilities. Regularly updating and patching your system remains the best defense against newly discovered threats. Stay vigilant, and always practice good cybersecurity hygiene.

Timeline

Published on: 04/16/2024 16:15:08 UTC
Last modified on: 07/03/2024 02:06:08 UTC