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Fencer Intel
medium 6.4

CVE-2015-4520 json

Mozilla Firefox before 41.0 and Firefox ESR 38.x before 38.3 allow remote attackers to bypass CORS preflight protection mechanisms by lever…

published 2015-09-24 11 y ago modified 2026-06-17 4 mo ago also EUVD-2015-4540

cvss
6.4
version 2.0, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.6%
EPSS 2.6% chance of exploitation in 30 days, percentile 85%
public exploits
0
none known

Summary

Mozilla Firefox before 41.0 and Firefox ESR 38.x before 38.3 allow remote attackers to bypass CORS preflight protection mechanisms by leveraging (1) duplicate cache-key generation or (2) retrieval of a value from an incorrect HTTP Access-Control-* response header.

Patch / fix

  • firefox Ubuntu 14.04 LTS 41.0+build3-0ubuntu0.14.04.1
  • thunderbird Ubuntu 14.04 LTS 1:38.3.0+build1-0ubuntu0.14.04.1

ubuntu advisories UBUNTU-CVE-2015-4520

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • thunderbird RHEL 5 PRODUCTIVITY, RHEL 5 38.3.0-1.el5_11
  • thunderbird RHEL 6 38.3.0-1.el6_7
  • thunderbird RHEL 7 38.3.0-1.el7_1
  • thunderbird RHEL 7 38.3.0-1.ael7b_1
  • firefox RHEL 5 38.3.0-2.el5_11
  • firefox RHEL 6 38.3.0-2.el6_7
  • firefox RHEL 7 38.3.0-2.el7_1

red hat advisories RHSA-2015:1852RHSA-2015:1834

  • MozillaFirefox SLES for SAP 11 SP4, SLES for SAP 11 SP3, SLES 11 SP4 +6 more 38.3.0esr-22.1
  • mozilla-nspr SLES for SAP 12, SLES 12, SLED 12 +1 more 4.10.9-6.1
  • MozillaFirefox SLES for SAP 12, SLES 12, SLED 12 +1 more 38.3.0esr-48.1

suse advisories SUSE-SU-2015:1703-1SUSE-SU-2015:1680-1

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 50.1.0-1.1
  • MozillaThunderbird openSUSE Tumbleweed 45.5.1-1.1

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10071-1openSUSE-SU-2024:10230-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2015-4520 updated cvss 6.8

Mozilla: Errors in the handling of CORS preflight request headers (MFSA 2015-111)

  • Red Hat Enterprise Linux (v. 5 server) firefox 38.3.0-2.el5_11 Red Hat Enterprise Linux Client (v. 7) firefox 38.3.0-2.el7_1, thunderbird 38.3.0-1.el7_1 Red Hat Enterprise Linux Client Optional (v. 7) firefox 38.3.0-2.el7_1 Red Hat Enterprise Linux Desktop (v. 5 client) firefox 38.3.0-2.el5_11, thunderbird 38.3.0-1.el5_11 Red Hat Enterprise Linux Desktop (v. 6) firefox 38.3.0-2.el6_7, thunderbird 38.3.0-1.el6_7 Red Hat Enterprise Linux Desktop Optional (v. 6) firefox 38.3.0-2.el6_7
    +1 more products
    Red Hat Enterprise Linux HPC Node Optional (v. 6) firefox 38.3.0-2.el6_7
    fixed: vendor fix RHSA-2015:1834
  • Red Hat Enterprise Linux Optional Productivity Applications (v. 5 server) thunderbird 38.3.0-1.el5_11
    fixed: vendor fix RHSA-2015:1852
  • Red Hat Enterprise Linux Server (v. 6) firefox 38.3.0-2.el6_7 Red Hat Enterprise Linux Server (v. 7) firefox 38.3.0-2.el7_1, firefox 38.3.0-2.ael7b_1 Red Hat Enterprise Linux Server Optional (v. 6) firefox 38.3.0-2.el6_7, thunderbird 38.3.0-1.el6_7 Red Hat Enterprise Linux Server Optional (v. 7) firefox 38.3.0-2.el7_1, thunderbird 38.3.0-1.el7_1, thunderbird 38.3.0-1.ael7b_1 Red Hat Enterprise Linux Workstation (v. 6) firefox 38.3.0-2.el6_7, thunderbird 38.3.0-1.el6_7 Red Hat Enterprise Linux Workstation (v. 7) firefox 38.3.0-2.el7_1, thunderbird 38.3.0-1.el7_1
    +2 more products
    Red Hat Enterprise Linux Workstation Optional (v. 6) firefox 38.3.0-2.el6_7 Red Hat Enterprise Linux Workstation Optional (v. 7) firefox 38.3.0-2.el7_1
    fixed: vendor fix RHSA-2015:1834

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

2.61% chance of exploitation in the next 30 days, higher than 85% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 2.0 6.4 AV:N/AC:L/Au:N/C:P/I:P/A:N

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.