Auth bypass in Mozilla Firefox
CVE-2021-38503
The iframe sandbox rules were not correctly applied to XSLT stylesheets, allowing an iframe to bypass restrictions such as executing scripts or navigating the top-level frame. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 10.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.038 (89.7th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 90th percentile — 89.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.038 · newest: 0.038 · change: 0.000
Affected products
- Mozilla Firefox — versions unspecified
- Mozilla Firefox Esr — versions unspecified
- Mozilla Firefox Esr
- Mozilla Thunderbird — versions unspecified
- Debian Linux — versions 9.0, 10.0, 11.0
Weakness classification (CWE)
Public proof-of-concept exploits
References
- www.mozilla.org/security/advisories/mfsa2021-49/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2021-50/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2021-48/ (Vendor Advisory)
- bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking, Vendor Advisory)
- www.debian.org/security/2021/dsa-5026 (vendor-advisory, Third Party Advisory)
- lists.debian.org/debian-lts-announce/2021/12/msg00030.html (mailing-list, Mailing List, Third Party Advisory)
- www.debian.org/security/2022/dsa-5034 (vendor-advisory, Third Party Advisory)
- lists.debian.org/debian-lts-announce/2022/01/msg00001.html (mailing-list, Mailing List, Third Party Advisory)
- security.gentoo.org/glsa/202202-03 (vendor-advisory, Third Party Advisory)
- security.gentoo.org/glsa/202208-14 (vendor-advisory, Third Party Advisory)
Frequently asked questions
- What is CVE-2021-38503?
- CVE-2021-38503 is a critical-severity vulnerability in Mozilla Firefox, classified under Incorrect Authorization. CVSS score: 10.0/10. Published 2021-12-08.
- How severe is CVE-2021-38503?
- Critical severity. CVSS v3 base score is 10.0 out of 10.
- Is CVE-2021-38503 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.