How severe is CVE-2026-47736?

CVE-2026-47736 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-47736?

CVE-2026-47736 affects the following packages: puma (RubyGems), puma (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2026-47736?

Update puma to 8.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-47736 is resolved across your whole dependency graph.

How do I detect CVE-2026-47736 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for puma, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-47736 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-47736 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-47736 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-47736?

CVE-2026-47736 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 26th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-47736?

CVE-2026-47736 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-47736 published, and has it been updated?

CVE-2026-47736 was published on July 14, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎

💎 RubyGems

Not in CISA KEV

HIGH severity

CVE-2026-47736 — puma

HIGHFix: puma/puma@439c613

CVE-2026-47736 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in puma. A fix is available for puma — see the affected versions and patch details below.

Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion

Also known asGHSA-qpgp-93vx-g8v8

Published

Jul 14, 2026

Updated

Aug 12, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 12, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-47736.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk-0.28%

Lower risk than most CVEs26th percentile — riskier than 26% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-47736 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 388,997 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected

💎puma💎puma

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

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

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`puma`	≥ 8.0.0&&< 8.0.2	8.0.2`bundle update puma --conservative`
💎RubyGems	`puma`	≥ 5.5.0&&< 7.2.1	7.2.1`bundle update puma --conservative`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for puma, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update puma to 8.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-47736 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This issue only affects Puma deployments that explicitly enable the non-default proxy_protocol: :v1 remote-address configuration (set_remote_address proxy_protocol: :v1). An unauthenticated network attacker able to open a TCP connection to such a listener can send bytes without a terminating CRLF, causing unbounded…

Workaround published by Red Hat

Upgrade to Puma 7.2.1 (7.x branch) or 8.0.2 (8.x branch), whichever applies to the deployed release line. If an immediate upgrade is not possible, remove or comment out the set_remote_address proxy_protocol: :v1 configuration directive if it is not required, or restrict direct network access to the affected Puma listener to trusted load balancers or reverse proxies only.

Source: Red Hat security advisory for CVE-2026-47736 (CC BY 4.0)

Frequently Asked Questions

### 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