CVE-2023-50269Public exploitNetwork attack vector

Unauthenticated proxy crash via recursive X-Forwarded-For ACL checks

Published Dec 14, 2023 · Updated May 21, 2025

Uncontrolled recursion in Squid 2.6 through 2.7.STABLE9, 3.1 through 5.9, and 6.0.1 through 6.5 allows remote attackers to crash the proxy. clientFollowXForwardedForCheck repeatedly invokes an immediate ACL callback for each accepted X-Forwarded-For address without limiting the number of hops, eventually exhausting the Squid process stack. The request requires follow_x_forwarded_for to be configured, and a successful attack interrupts the single-process proxy service.

CVSS severity8.6
High
EPSS probability57.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled recursion in Squid 2.6 through 2.7.STABLE9, 3.1 through 5.9, and 6.0.1 through 6.5 allows remote attackers to crash the proxy. clientFollowXForwardedForCheck repeatedly invokes an immediate ACL callback for each accepted X-Forwarded-For address without limiting the number of hops, eventually exhausting the Squid process stack. The request requires follow_x_forwarded_for to be configured, and a successful attack interrupts the single-process proxy service.

The record

CVE
CVE-2023-50269
Published
Dec 14, 2023
Updated
May 21, 2025
Vendor
The Squid Software Foundation
Product
Squid
Classifications
CWE-674, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 14, 2023CVE publishedPublication date reported by the CVE source.
  2. May 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 2.6, <= 2.7.STABLE9
  2. Affected versionversion=>= 3.1, <= 5.9
  3. Affected versionversion=>= 6.0.1, < 6.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Squid Software Foundation · Squidversion=>= 2.6, <= 2.7.STABLE9; version=>= 3.1, <= 5.9; version=>= 6.0.1, < 6.6

Published CVSS scores

8.6GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
7.5NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-674Uncontrolled Recursion
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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