What is CVE-2020-6798?

CVE-2020-6798 is a medium-severity vulnerability in Mozilla Firefox, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2020-03-02.

How severe is CVE-2020-6798?

Medium severity. CVSS v3 base score is 6.1 out of 10.

Is CVE-2020-6798 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

XSS in Mozilla Firefox

CVE-2020-6798

If a template tag was used in a select tag, the parser could be confused and allow JavaScript parsing and execution when it should not be allowed. A site that relied on the browser behaving correctly could suffer a cross-site scripting vulnerability as a result. In general, this flaw cannot be exploited through email in the Thunderbird product because scripting is disabled when reading mail, but is potentially a risk in browser or browser-like contexts. This vulnerability affects Thunderbird < 68.5, Firefox < 73, and Firefox < ESR68.5.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2020-03-02 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.021 (81.3th percentile), scored 2026-10-02.

Low probability of exploitation in the next 30 days, but still tracked. 81st percentile — 81.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.021 · newest: 0.021 · change: +0.001

Affected products

Mozilla Firefox — versions unspecified
Mozilla Firefox Esr
Mozilla Thunderbird — versions unspecified

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

ARPSyndicate/cvemon

References

www.mozilla.org/security/advisories/mfsa2020-05/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2020-06/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2020-07/ (Vendor Advisory)
bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
usn.ubuntu.com/4278-2/ (vendor-advisory)
security.gentoo.org/glsa/202003-02 (vendor-advisory)
security.gentoo.org/glsa/202003-10 (vendor-advisory)
usn.ubuntu.com/4328-1/ (vendor-advisory)
usn.ubuntu.com/4335-1/ (vendor-advisory)

Frequently asked questions

What is CVE-2020-6798?: CVE-2020-6798 is a medium-severity vulnerability in Mozilla Firefox, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2020-03-02.
How severe is CVE-2020-6798?: Medium severity. CVSS v3 base score is 6.1 out of 10.
Is CVE-2020-6798 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.