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CVE-2026-47736

Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion

7.5 HighFix available

Puma is a Ruby/Rack web server built for parallelism. From 5.5.0 until 7.2.1 and 8.0.2, when PROXY protocol v1 support is enabled, Puma reads incoming bytes into an internal buffer while waiting for CRLF to determine whether a PROXY v1 line is present, allowing an attacker that continuously sends bytes without CRLF to cause unbounded in-process memory growth and additional CPU cost from repeatedly scanning the growing buffer. This issue is fixed in versions 7.2.1 and 8.0.2.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

0.35%Up 0.3 points since Jun 12, 2026
90%50%10%1%

What each source reports

CVE List Score used 7.5

Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion

Puma is a Ruby/Rack web server built for parallelism. From 5.5.0 until 7.2.1 and 8.0.2, when PROXY protocol v1 support is enabled, Puma reads incoming bytes into an internal buffer while waiting for CRLF to determine whether a PROXY v1 line is present, allowing an attacker that continuously sends bytes without CRLF to cause unbounded in-process memory growth and additional CPU cost from repeatedly scanning the growing buffer. This issue is fixed in versions 7.2.1 and 8.0.2.

Record
CVE-2026-47736
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-02
EUVDEUVD-2026-44442 7.5

Puma is a Ruby/Rack web server built for parallelism. From 5.5.0 until 7.2.1 and 8.0.2, when PROXY protocol v1 support is enabled, Puma reads incoming bytes into an internal buffer while waiting for CRLF to determine whether a PROXY v1 line is present, allowing an attacker that continuously sends bytes without CRLF to cause unbounded in-process memory growth and additional CPU cost from repeatedly scanning the growing buffer. This issue is fixed in versions 7.2.1 and 8.0.2.

Record
EUVD-2026-44442
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-qpgp-93vx-g8v8 7.5

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

Record
GHSA-qpgp-93vx-g8v8
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-03
NVD 7.5

Puma is a Ruby/Rack web server built for parallelism. From 5.5.0 until 7.2.1 and 8.0.2, when PROXY protocol v1 support is enabled, Puma reads incoming bytes into an internal buffer while waiting for CRLF to determine whether a PROXY v1 line is present, allowing an attacker that continuously sends bytes without CRLF to cause unbounded in-process memory growth and additional CPU cost from repeatedly scanning the growing buffer. This issue is fixed in versions 7.2.1 and 8.0.2.

Record
CVE-2026-47736
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-02
OSV 7.5

Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion

Puma is a Ruby/Rack web server built for parallelism. From 5.5.0 until 7.2.1 and 8.0.2, when PROXY protocol v1 support is enabled, Puma reads incoming bytes into an internal buffer while waiting for CRLF to determine whether a PROXY v1 line is present, allowing an attacker that continuously sends bytes without CRLF to cause unbounded in-process memory growth and additional CPU cost from repeatedly scanning the growing buffer. This issue is fixed in versions 7.2.1 and 8.0.2.

Record
CVE-2026-47736
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-02
OSVDEBIAN-CVE-2026-47736 7.5

Puma is a Ruby/Rack web server built for parallelism. From 5.5.0 until 7.2.1 and 8.0.2, when PROXY protocol v1 support is enabled, Puma reads incoming bytes into an internal buffer while waiting for CRLF to determine whether a PROXY v1 line is present, allowing an attacker that continuously sends bytes without CRLF to cause unbounded in-process memory growth and additional CPU cost from repeatedly scanning the growing buffer. This issue is fixed in versions 7.2.1 and 8.0.2.

Record
DEBIAN-CVE-2026-47736
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVGHSA-qpgp-93vx-g8v8 7.5

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

Record
GHSA-qpgp-93vx-g8v8
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-03
OSVUBUNTU-CVE-2026-47736 7.5

Puma is a Ruby/Rack web server built for parallelism. From 5.5.0 until 7.2.1 and 8.0.2, when PROXY protocol v1 support is enabled, Puma reads incoming bytes into an internal buffer while waiting for CRLF to determine whether a PROXY v1 line is present, allowing an attacker that continuously sends bytes without CRLF to cause unbounded in-process memory growth and additional CPU cost from repeatedly scanning the growing buffer. This issue is fixed in versions 7.2.1 and 8.0.2.

Record
UBUNTU-CVE-2026-47736
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
puma
RubyGems
 8.0.0 up to 8.0.2
8.0.2
puma
RubyGems
 5.5.0 up to 7.2.1
7.2.1
puma
Debian:12
 before 5.6.5-3+deb12u2, plus listed versions
5.6.5-35.6.5-3+deb12u1
5.6.5-3+deb12u2
puma
Debian:13
 All versions, plus listed versions
6.6.0-48.0.2-18.0.2-28.0.2-3
 None known
puma
Debian:14
 before 8.0.2-1, plus listed versions
6.6.0-4
8.0.2-1
puma
RubyGems
 8.0.0 up to 8.0.2, plus listed versions
8.0.1
8.0.2
puma
RubyGems
 5.5.0 up to 7.2.1, plus listed versions
5.5.15.5.25.6.05.6.15.6.2
Show 31 moreShow less
5.6.45.6.55.6.65.6.75.6.85.6.96.0.06.0.16.0.26.1.06.1.16.2.06.2.16.2.26.3.06.3.16.4.06.4.16.4.26.4.36.5.06.6.06.6.17.0.07.0.0.pre17.0.17.0.27.0.37.0.47.1.07.2.0
7.2.1
puma
Ubuntu:Pro:20.04:LTS
 All versions, plus listed versions
3.12.0-2ubuntu13.12.0-4ubuntu13.12.4-1ubuntu23.12.4-1ubuntu2+esm13.12.4-1ubuntu2+esm2
 None known
puma
Ubuntu:Pro:22.04:LTS
 All versions, plus listed versions
4.3.6-1ubuntu45.5.2-2ubuntu25.5.2-2ubuntu2+esm15.5.2-2ubuntu2+esm2
 None known
puma
Ubuntu:24.04:LTS
 All versions, plus listed versions
5.6.5-4ubuntu25.6.5-4ubuntu36.4.2-4ubuntu16.4.2-4ubuntu36.4.2-4ubuntu46.4.2-4ubuntu4.3
 None known
puma
Ubuntu:26.10
 All versions, plus listed versions
6.6.0-4build18.0.2-3build1
 None known
puma
Ubuntu:26.04:LTS
 All versions, plus listed versions
6.6.0-46.6.0-4build1
 None known

History

History
RecordedChangedSources
referencesGitHub Advisories, OSV
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-47736 is a high vulnerability (CVSS 7.5) in Puma, published June 8, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.35%, the 28th percentile. Fixed in puma 8.0.2.

References

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