CVE-2018-18506

CVE-2018-18506 is a medium-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 5.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

• Severity: Medium (CVSS 3.x base score 5.9)
• CVSS v2: 4.3
• EPSS exploit prediction: 2% (80th percentile)
• Actively exploited: Not listed in CISA KEV
• Affected product: Mozilla Firefox
• Published: 2019-02-05
• Last modified: 2026-06-17

Description

When proxy auto-detection is enabled, if a web server serves a Proxy Auto-Configuration (PAC) file or if a PAC file is loaded locally, this PAC file can specify that requests to the localhost are to be sent through the proxy to another server. This behavior is disallowed by default when a proxy is manually configured, but when enabled could allow for attacks on services and tools that bind to the localhost for networked behavior if they are accessed through browsing. This vulnerability affects Firefox < 65.

Frequently asked questions

What is CVE-2018-18506?

When proxy auto-detection is enabled, if a web server serves a Proxy Auto-Configuration (PAC) file or if a PAC file is loaded locally, this PAC file can specify that requests to the localhost are to be sent through the proxy to another server. This behavior is disallowed by default when a proxy is manually configured, but when enabled could allow for attacks on services and tools that bind to the localhost for networked behavior if they are accessed through browsing. This vulnerability affects Firefox < 65.

How severe is CVE-2018-18506?

CVE-2018-18506 has a CVSS 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2018-18506 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-18506?

CVE-2018-18506 primarily affects Mozilla Firefox. In total, 29 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2018-18506?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2018-18506 published?

CVE-2018-18506 was published on 2019-02-05 and last updated on 2026-06-17.

References

• http://lists.opensuse.org/opensuse-security-announce/2019-03/msg00035.html
• http://lists.opensuse.org/opensuse-security-announce/2019-03/msg00043.html
• http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00023.html
• http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00043.html
• http://www.securityfocus.com/bid/106773
• https://access.redhat.com/errata/RHSA-2019:0622
• https://access.redhat.com/errata/RHSA-2019:0623
• https://access.redhat.com/errata/RHSA-2019:0680
• https://access.redhat.com/errata/RHSA-2019:0681
• https://access.redhat.com/errata/RHSA-2019:0966
• https://access.redhat.com/errata/RHSA-2019:1144
• https://lists.debian.org/debian-lts-announce/2019/03/msg00024.html
• https://lists.debian.org/debian-lts-announce/2019/04/msg00000.html
• https://seclists.org/bugtraq/2019/Apr/0
• https://seclists.org/bugtraq/2019/Mar/28
• https://security.gentoo.org/glsa/201904-07
• https://usn.ubuntu.com/3874-1/
• https://usn.ubuntu.com/3927-1/
• https://www.debian.org/security/2019/dsa-4411
• https://www.debian.org/security/2019/dsa-4420
• https://www.mozilla.org/security/advisories/mfsa2019-01/

Affected products (29)

• cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:lts:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*
• cpe:2.3:o:canonical:ubuntu_linux:18.10:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:8.0:*:*:*:*:*:*:*
• cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_desktop:6.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_desktop:7.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_eus:8.1:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_eus:8.2:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_eus:8.4:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_eus:8.6:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server:6.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server:7.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_aus:7.6:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_aus:8.2:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_aus:8.4:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_aus:8.6:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_eus:7.6:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_tus:7.6:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_tus:8.2:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_tus:8.4:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_server_tus:8.6:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_workstation:6.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux_workstation:7.0:*:*:*:*:*:*:*
• cpe:2.3:o:opensuse:leap:15.0:*:*:*:*:*:*:*
• cpe:2.3:o:opensuse:leap:42.3:*:*:*:*:*:*:*

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