CVE-2023-49288 | Denial of Service in HTTP Collapsed Forwarding in Squid

Squid is a caching proxy for the Web supporting HTTP, HTTPS, FTP, and more. Affected versions of squid are subject to a a Use-After-Free bug which can lead to a Denial of Service attack via collapsed forwarding. All versions of Squid from 3.5 up to and including 5.9 configured with "collapsed_forwarding on" are vulnerable. Configurations with "collapsed_forwarding off" or without a "collapsed_forwarding" directive are not vulnerable. This bug is fixed by Squid version 6.0.1. Users are advised to upgrade. Users unable to upgrade should remove all collapsed_forwarding lines from their squid.conf.

Published: 2023-12-04 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2023-49288 is rated High Risk (68.8/100): CVSS High severity, with high exploitation likelihood (EPSS 4.78%, 91th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +2.68% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2023-49288

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 2.10% 4.78% +2.68%
2 2026-01-16 2.89% 2.10% -0.79%
3 2025-12-28 — 2.89% —

Full EPSS history (27 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2023-49288

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.6 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 4.0 [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2023-49288

OS Trackers for CVE-2023-49288

vendor priority summary link
alpine — CVE-2023-49288: 1 source package rows (squid); 57 state rows across 7 repos (3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 5, open 52. https://security.alpinelinux.org/vuln/CVE-2023-49288
debian not yet assigned CVE-2023-49288 not yet assigned priority: Debian including 1 source packages (squid), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 3, open 2. https://security-tracker.debian.org/tracker/CVE-2023-49288
redhat medium — https://access.redhat.com/security/cve/CVE-2023-49288
suse medium CVE-2023-49288 severity moderate: SUSE including 5 source package names (squid, squid-6.10-150600.3.6.1, squid-6.12-160000.2.2, squid-6.6-2.1, squid3), 36 product×package rows across 35 product lines (SUSE CaaS Platform 4.0, SUSE Enterprise Storage 7.1, … (35 product lines)): Known Not Affected 33, Fixed 3. https://www.suse.com/security/cve/CVE-2023-49288/
ubuntu medium CVE-2023-49288 medium priority: Ubuntu including 2 source packages (squid, squid3), 24 status rows across 12 suites (bionic, focal, jammy, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 8, ignored 5, not-affected 5, released 3, needed 2, needs-triage 1. https://ubuntu.com/security/CVE-2023-49288

Affected software / configurations for CVE-2023-49288

Vendor Product Version Raw CPE
squid-cache squid >= 3.5, <= 5.9 cpe:2.3:a:squid-cache:squid:*:*:*:*:*:*:*:*

References for CVE-2023-49288

cvelogic Threat Intelligence