🛡️ CVE-2026-47736 — puma

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-400 NVD
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion

Impact

[PROXY protocol support for Puma](https://github.com/puma/puma/issues/2651) 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:

```ruby

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:

```ruby

# 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](https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt)
  • [CWE-400: Uncontrolled Resource Consumption](https://cwe.mitre.org/data/definitions/400.html)
  • [CWE-770: Allocation of Resources Without Limits or Throttling](https://cwe.mitre.org/data/definitions/770.html)
  • [Puma set_remote_address documentation](https://github.com/puma/puma/blob/master/lib/puma/dsl.rb)
  • [Puma client PROXY protocol parsing code](https://github.com/puma/puma/blob/master/lib/puma/client.rb)
  • [Puma constants, including PROXY_PROTOCOL_V1_REGEX](https://github.com/puma/puma/blob/master/lib/puma/const.rb)

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

Weakness class

CVE-2026-47736 is classified as CWE-400: Uncontrolled Resource Consumption. A request can consume memory, CPU or storage without limit, exhausting capacity for everyone else.

Affected software

CVE-2026-47736 is recorded against 2 packages.

  • puma (from 5.5.0 up to 7.2.1)
  • unknown

Timeline and source

Published on 8 June 2026 and last revised on 10 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com (Web)
github.com (Package)
github.com (Web)
www.cve.org (Web)

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-400
Public Exploit ✅ No
Source NVD
Published 2026-06-08
Updated 2026-08-12
Modified 2026-06-10
Fix URL N/A

Affected Packages

Software From version Fixed in
puma 5.5.0 7.2.1
unknown — —

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