CVE-2026-47737

Puma PROXY Protocol v1 Accepts Repeated Protocol Headers on Persistent Connections

Workarounds

Disable PROXY protocol v1 parsing if it is not required:

  # remove/comment this:
  # set_remote_address proxy_protocol: :v1

Users can also disable persistent connections to Puma, for example:

enable_keep_alives false

References

• HAProxy PROXY protocol specification
• CVE-2025-31135 / GHSA-c2c3-pqw5-5p7c: go-guerrilla repeated PROXY command source IP spoofing
• Puma set_remote_address documentation

Puma is vulnerable to source IP spoofing when set_remote_address proxy_protocol: :v1 is enabled and persistent connections are used.

PROXY protocol v1 is a connection-level protocol. Support was added to Puma in v5.5.0. A proxy sends one PROXY header at the beginning of a TCP connection, before any HTTP data. Puma incorrectly re-parsed PROXY protocol headers after each keep-alive request on the same connection. An attacker able to send HTTP requests through a trusted proxy could therefore inject a second PROXY header between HTTP requests. Puma would treat the injected header as authoritative for the next request and overwrite REMOTE_ADDR.

This can mislead applications or middleware that use REMOTE_ADDR for security decisions, rate limiting, auditing, or allow/deny lists.

Only deployments that explicitly enable PROXY protocol v1 are affected, and will have set:

set_remote_address proxy_protocol: :v1

Puma's default configuration is not affected. Deployments that do not use persistent connections to Puma are also not expected to be affected by this issue.

CVE-2026-47737 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (8.0.2, 7.2.1); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Users should upgrade to versions 7.2.1 or 8.0.2.

1. What is CVE-2026-47737? CVE-2026-47737 is a high-severity security vulnerability in puma (rubygems), affecting versions >= 8.0.0, < 8.0.2. It is fixed in 8.0.2, 7.2.1.
2. How severe is CVE-2026-47737? CVE-2026-47737 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of puma are affected by CVE-2026-47737? puma (rubygems) versions >= 8.0.0, < 8.0.2 is affected.
4. Is there a fix for CVE-2026-47737? Yes. CVE-2026-47737 is fixed in 8.0.2, 7.2.1. Upgrade to this version or later.
5. Is CVE-2026-47737 exploitable, and should I be worried? Whether CVE-2026-47737 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-47737 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-47737?
   • Upgrade puma to 8.0.2 or later
   • Upgrade puma to 7.2.1 or later

Other vulnerabilities in puma