CVE-2023-49288Network attack vector

Service crash via collapsed-forwarding use-after-free

Published Dec 4, 2023 · Updated Feb 13, 2025

Use-after-free in HTTP collapsed forwarding in Squid 3.5 through 5.9 allows remote attackers to crash the proxy service. The upstream advisory does not identify the freed object, lifetime error, or request sequence that triggers the stale reference. Unauthenticated network access is sufficient, but only deployments explicitly configured with collapsed_forwarding on are exposed.

CVSS severity8.6
High
EPSS probability4.78%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in HTTP collapsed forwarding in Squid 3.5 through 5.9 allows remote attackers to crash the proxy service. The upstream advisory does not identify the freed object, lifetime error, or request sequence that triggers the stale reference. Unauthenticated network access is sufficient, but only deployments explicitly configured with collapsed_forwarding on are exposed.

The record

CVE
CVE-2023-49288
Published
Dec 4, 2023
Updated
Feb 13, 2025
Vendor
The Squid Software Foundation
Product
Squid
Classifications
CWE-416, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 4, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=>= 3.5, < 6.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Squid Software Foundation · Squidversion=>= 3.5, < 6.0.1

Published CVSS scores

8.6GitHub, Inc.CVSS: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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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