Summary
Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion
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
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
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-47736 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.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Users should upgrade to versions 7.2.1 or 8.0.2.
Frequently Asked Questions
- What is CVE-2026-47736? CVE-2026-47736 is a high-severity uncontrolled resource consumption vulnerability in puma (rubygems), affecting versions >= 8.0.0, < 8.0.2. It is fixed in 8.0.2, 7.2.1. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-47736? CVE-2026-47736 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.
- Which versions of puma are affected by CVE-2026-47736? puma (rubygems) versions >= 8.0.0, < 8.0.2 is affected.
- Is there a fix for CVE-2026-47736? Yes. CVE-2026-47736 is fixed in 8.0.2, 7.2.1. Upgrade to this version or later.
- Is CVE-2026-47736 exploitable, and should I be worried? Whether CVE-2026-47736 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
- What actually determines whether CVE-2026-47736 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.
- How do I fix CVE-2026-47736?
- Upgrade
pumato 8.0.2 or later - Upgrade
pumato 7.2.1 or later
- Upgrade