CVE-2026-47736High· 7.5▾ TwilightPuma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 41.3 · likelihood 0.1 · exploitation 0
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Exploit-prediction probability, daily snapshots since Jul 15.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via GHSA
0.4%
0.4% → 0.6%
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
Users should upgrade to versions 7.2.1 or 8.0.2.
# remove/comment this:
# set_remote_address proxy_protocol: :v1
set_remote_address documentationPROXY_PROTOCOL_V1_REGEXpuma >= 8.0.0, < 8.0.2puma >= 5.5.0, < 7.2.1Upgrade to a patched release:
puma 8.0.2puma 7.2.1Connected by shared product, vendor, weakness, or advisory.
CVE-2026-47737High· 7.5Puma PROXY Protocol v1 Accepts Repeated Protocol Headers on Persistent Connections
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