Resource exhaustion in Puma

CVE-2026-47736

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.

Vulnerability class: DoS (Denial of Service)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.003 (26.9th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 27th percentile — 26.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-47736: held from 0.006 to 0.003.

EPSS over last 30 days · oldest: 0.006 · newest: 0.003 · change: -0.003

Affected products

  • Puma — versions >= 5.5.0, < 7.2.1, >= 8.0.0, < 8.0.2

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-47736?
CVE-2026-47736 is a high-severity vulnerability in Puma, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-07-14.
How severe is CVE-2026-47736?
High severity. CVSS v3 base score is 7.5 out of 10.