🚨 Puma PROXY Protocol v1 Accepts Repeated Protocol Headers on Persistent Connections

Impact

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.

Patches

Users should upgrade to versions 7.2.1 or 8.0.2.

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 PROXY Protocol v1 Parser Allows Remote Memory Exhaustion

Impact

PROXY protocol support for Puma was added in version 5.5.0.

When PROXY protocol v1 support is enabled, Puma reads incoming bytes into an internal buffer. It waits for "\r\n" to determine whether a PROXY v1 line is present. If an attacker opens a TCP connection and continuously sends bytes without CRLF, Puma keeps appending to this pre-parse buffer.

This can cause unbounded in-process memory growth and additional CPU cost from repeatedly scanning the growing buffer for CRLF. A single, unauthenticated TCP connection can drive significant memory growth and may cause process/container OOM or degraded availability.

Only Puma servers using the following non-default config are affected:

   set_remote_address proxy_protocol: :v1

Patches

Users should upgrade to versions 7.2.1 or 8.0.2.

Workarounds

• Disable PROXY protocol v1 parsing if it is not required:

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

• Restrict direct network access to Puma listeners using PROXY protocol:
  • Only allow trusted load balancers/reverse proxies to connect.
  • Block arbitrary client TCP access with firewall/security group rules.

Resources

• HAProxy PROXY protocol specification
• CWE-400: Uncontrolled Resource Consumption
• CWE-770: Allocation of Resources Without Limits or Throttling
• Puma set_remote_address documentation
• Puma client PROXY protocol parsing code
• Puma constants, including PROXY_PROTOCOL_V1_REGEX

7.2.1

• Bugfixes
  • Limit and anchor PROXY protocol v1 parsing to prevent abuse via crafted inputs ([#3947])
  • Parse PROXY protocol only once per connection to prevent injection on keep-alive requests ([#3947])

Security advisories

• CVE-2026-47736 / GHSA-qpgp-93vx-g8v8: Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion
• CVE-2026-47737 / GHSA-2vqw-3mp8-cgmx: Puma PROXY Protocol v1 Accepts Repeated Protocol Headers on Persistent Connections

Does any of this look wrong? Please let us know.

See the full diff on Github. The new version differs by 2 commits:

• Release v7.2.1 (#3948)
• 7.2.1 backport (#3947)

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