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Response snapshot Nov 2, 2026, 23:21 UTC

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VulnerabilityCVE-2026-47736

Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion

[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.

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
0.3% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: puma: 8.0.2; puma: 7.2.1. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-qpgp-93vx-g8v8 (opens a new tab)

What happened

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.

Continue reading

Only Puma servers using the following non-default config are affected:

 set_remote_address proxy_protocol: :v1

Patches

Users should upgrade to versions 7.2.1 or 8.0.2.

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

- [HAProxy PROXY protocol specification](https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt) - [CWE-400: Uncontrolled Resource Consumption](https://cwe.mitre.org/data/definitions/400.html) - [CWE-770: Allocation of Resources Without Limits or Throttling](https://cwe.mitre.org/data/definitions/770.html) - [Puma set_remote_address documentation](https://github.com/puma/puma/blob/master/lib/puma/dsl.

rb) - [Puma client PROXY protocol parsing code](https://github.com/puma/puma/blob/master/lib/puma/client.rb) - [Puma constants, including PROXY_PROTOCOL_V1_REGEX](https://github.com/puma/puma/blob/master/lib/puma/const.rb)

Affected package ranges reported by GitHub: puma: >= 8.0.0, < 8.0.2 puma: >= 5.5.0, < 7.2.1

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.3%

Scored Percentile 28.2%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-qpgp-93vx-g8v8 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-qpgp-93vx-g8v8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-47736, scored 2026-11-02. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 2). Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion (CVE-2026-47736). https://kevwire.com/record/CVE-2026-47736

MLA

"Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion (CVE-2026-47736)." KEVWire, 2 Nov. 2026, kevwire.com/record/CVE-2026-47736.

Chicago

KEVWire. "Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion (CVE-2026-47736)." Last modified November 2, 2026. https://kevwire.com/record/CVE-2026-47736.

Evidence summary (plain text)

Puma PROXY Protocol v1 Parser Allows Remote Memory Exhaustion (Jun 8, 2026).
[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.
CVSS 7.5 (version 3.1; evidence as of Nov 2, 2026; https://github.com/advisories/GHSA-qpgp-93vx-g8v8).
EPSS 0.3% for the following 30 days, scored Nov 2, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-47736&date=2026-11-02).
Sources:
GitHub-reviewed advisory GHSA-qpgp-93vx-g8v8: https://github.com/advisories/GHSA-qpgp-93vx-g8v8
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-47736&date=2026-11-02
Record ID: CVE-2026-47736.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 2, 2026, 23:21 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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