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CVE-2024-21647VulnerabilityPublished Updated

CVE-2024-21647: puma · HTTP Request/Response Smuggling

Affects pumaSource CVE Database V5

0

Not known to be exploited · CVSS 5.9 Medium : upgrade to 6.4.2 or 5.6.8 when convenient.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score
5.9Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.9% chance of exploitation in 30 days – higher than 61% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 6.4.2, 5.6.8
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 8 Jan 2024

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

What to do

Upgrade puma to 6.4.2 or 5.6.8.

Affected software

ProductAffectedFixed in
RubyGemspumapkg:gem/pumaOther threatsAffected
  • <5.6.8
  • <6.4.2
Fixed in
  • 5.6.8
  • 6.4.2

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations should immediately audit their Puma server versions and upgrade to at least version 6.4.2 or 5.6.8 to ensure the vulnerability is patched. Beyond patching, organizations should implement strict input validation and limit HTTP request sizes at the web application firewall (WAF) or reverse proxy level to mitigate malformed requests. Deploying robust rate limiting and anomaly detection can help identify and block unusual request patterns indicative of smuggling attempts or resource exhaustion attacks. Network segmentation and isolating critical web services can reduce the blast radius of potential exploitation. Logging and monitoring HTTP request headers and chunk extensions can provide early indicators of attack attempts. Security teams should also review and update incident response plans to include scenarios involving HTTP request smuggling and DoS conditions. Finally, organizations should maintain an up-to-date inventory of Ruby/Rack applications using Puma to ensure comprehensive coverage of affected assets.

Description

Puma is a web server for Ruby/Rack applications built for parallelism. Prior to version 6.4.2, puma exhibited incorrect behavior when parsing chunked transfer encoding bodies in a way that allowed HTTP request smuggling. Fixed versions limits the size of chunk extensions. Without this limit, an attacker could cause unbounded resource (CPU, network bandwidth) consumption. This vulnerability has been fixed in versions 6.4.2 and 5.6.8.

References

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