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Vulnerability record · CVE-2018-1000027 · published 9 February 2018

CVE-2018-1000027: Squid-cache squid null pointer dereference vulnerability

Squid Cache · Squid

The Squid Software Foundation Squid HTTP Caching Proxy version prior to version 4.0.23 contains a NULL Pointer Dereference vulnerability in HTTP Response X-Forwarded-For header processing that can result in Denial of Service to all clients of the proxy. This attack appear to be exploitable via Remote HTTP server responding with an X-Forwarded-For header to certain types of HTTP request. This vulnerability appears to have been fixed in 4.0.23 and later.

7.5 CVSS 3.0 High EPSS 13% · top 3.8% CWE-476 · NULL pointer dereference
7.5CVSS 3.0 base score, v2 5.0
13%EPSS exploitation probability, 30 days
NoNot in CISA KEV
3Affected product versions listed by NVD
18References
17 Jun 2026Last modified by NVD

Description

The Squid Software Foundation Squid HTTP Caching Proxy version prior to version 4.0.23 contains a NULL Pointer Dereference vulnerability in HTTP Response X-Forwarded-For header processing that can result in Denial of Service to all clients of the proxy. This attack appear to be exploitable via Remote HTTP server responding with an X-Forwarded-For header to certain types of HTTP request. This vulnerability appears to have been fixed in 4.0.23 and later.

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

3 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://www.squid-cache.org/Advisories/SQUID-2018_2.txt PatchVendor Advisory
http://www.squid-cache.org/Versions/v3/3.5/changesets/SQUID-2018_2.patch PatchVendor Advisory
http://www.squid-cache.org/Versions/v4/changesets/SQUID-2018_2.patch PatchVendor Advisory
https://github.com/squid-cache/squid/pull/129/files Third Party Advisory
https://lists.debian.org/debian-lts-announce/2018/02/msg00001.html Mailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2018/02/msg00002.html Mailing ListThird Party Advisory
https://usn.ubuntu.com/3557-1/ Third Party Advisory
https://usn.ubuntu.com/4059-2/
https://www.debian.org/security/2018/dsa-4122 Third Party Advisory
http://www.squid-cache.org/Advisories/SQUID-2018_2.txt PatchVendor Advisory
http://www.squid-cache.org/Versions/v3/3.5/changesets/SQUID-2018_2.patch PatchVendor Advisory
http://www.squid-cache.org/Versions/v4/changesets/SQUID-2018_2.patch PatchVendor Advisory
https://github.com/squid-cache/squid/pull/129/files Third Party Advisory
https://lists.debian.org/debian-lts-announce/2018/02/msg00001.html Mailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2018/02/msg00002.html Mailing ListThird Party Advisory
https://usn.ubuntu.com/3557-1/ Third Party Advisory
https://usn.ubuntu.com/4059-2/
https://www.debian.org/security/2018/dsa-4122 Third Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2018-1000027), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.