CVE-2024-39316: Rack ReDoS Vulnerability in HTTP Accept Headers Parsing

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-07-02 · updated 2026-06-17
Weakness: CWE-1333

Description

Rack is a modular Ruby web server interface. Starting in version 3.1.0 and prior to version 3.1.5, Regular Expression Denial of Service (ReDoS) vulnerability exists in the `Rack::Request::Helpers` module when parsing HTTP Accept headers. This vulnerability can be exploited by an attacker sending specially crafted `Accept-Encoding` or `Accept-Language` headers, causing the server to spend excessive time processing the request and leading to a Denial of Service (DoS). The fix for CVE-2024-26146 was not applied to the main branch and thus while the issue was fixed for the Rack v3.0 release series, it was not fixed in the v3.1 release series until v3.1.5. Users of versions on the 3.1 branch should upgrade to version 3.1.5 to receive the fix.

Affected products

rack: from 3.1.0 before 3.1.5 — fixed in 3.1.5

How to fix

Upgrade to a fixed version: rack 3.1.5. Check the vendor advisory for mitigations.

References

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