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… (CVE-2026-47736)
Description
Puma versions from 5.5.0 until 7.2.1 and 8.0.2 have a vulnerability when PROXY protocol v1 support is enabled. The server reads incoming bytes into an internal buffer while waiting for a CRLF sequence to detect a PROXY v1 line. An attacker can exploit this by continuously sending bytes without CRLF, causing unbounded memory growth and increased CPU usage. This issue is fixed in versions 7.2.1 and 8.0.2.
CVSS v3.1
Score 7.5high
Affected software
pkg:deb/ubuntu/puma?arch=source&distro=esm-apps/focalpkg:deb/ubuntu/puma?arch=source&distro=esm-apps/jammypkg:deb/ubuntu/puma?arch=source&distro=noblepkg:deb/ubuntu/puma?arch=source&distro=stonkingpkg:deb/ubuntu/puma?arch=source&distro=resoluteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Puma, a Ruby/Rack web server, has a vulnerability identified as CVE-2026-47736 affecting versions from 5.5.0 up to but not including 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 a CRLF to determine the presence of a PROXY v1 line. An attacker can exploit this by sending a continuous stream of bytes without CRLF, leading to unbounded in-process memory growth and additional CPU cost due to repeated scanning of the growing buffer. This can cause denial of service conditions due to resource exhaustion. The vulnerability is resolved in Puma versions 7.2.1 and 8.0.2.
Potential Impact
The vulnerability allows an unauthenticated remote attacker to cause unbounded memory growth and increased CPU usage on the Puma server by sending continuous bytes without CRLF when PROXY protocol v1 support is enabled. This can lead to denial of service due to resource exhaustion. There is no impact on confidentiality or integrity reported.
Mitigation Recommendations
Upgrade Puma to version 7.2.1 or 8.0.2 or later where this issue is fixed. If upgrading is not immediately possible, consider disabling PROXY protocol v1 support to mitigate the risk. Patch status is confirmed fixed in versions 7.2.1 and 8.0.2.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-47736
- Osv Schema Version
- 1.7.0
- Ecosystems
- ["Ubuntu:Pro:20.04:LTS","Ubuntu:Pro:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:26.10","Ubuntu:26.04:LTS"]
- Cvss Version
- 3.1
Threat ID: 6ad3f6312cdf04f656664f0f
Added to database: 10/17/2026, 22:26:57 UTC
Last enriched: 10/18/2026, 01:08:46 UTC
Last updated: 10/18/2026, 01:08:46 UTC
Views: 2
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