CVE-2026-47736: Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion

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 "…

7.5CVSS Score

HIGHSeverity

NOCISA KEV

VulnerabilityImpact Type

📋 Vulnerability Details

CVE ID	CVE-2026-47736
Vendor	rubygems
Affected Product	puma
Vulnerability Type	Vulnerability
CVSS Score	7.5 (HIGH)
Actively Exploited	❌ No known exploitation
Patch Status	See Vendor Advisory →
Reported By	CYBERDUDEBIVASH SENTINEL APEX Intelligence (via github_advisories)

🔬 Technical Analysis

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 memory growth and may cause process/container OOM or degraded availability. Only Puma servers using the following non-default config are affected: ```ruby set_remote_address proxy_protocol: :v1`

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🎯 Known Indicators of Compromise

{"type":"url","value":"https://github.com/puma/puma/issues/2651)","confidence_score":0.82,"first_seen":"2026-06-09","source_count":1}

📚 Advisory References

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