A malicious webpage could have forced a Firefox for Android user into executing attacker-controlled JavaScript in the context of another do…

published 2021-06-24 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-16412

cvss: 6.1; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.6%; EPSS 0.6% chance of exploitation in 30 days, percentile 51%
public exploits: 0; none known

A malicious webpage could have forced a Firefox for Android user into executing attacker-controlled JavaScript in the context of another domain, resulting in a Universal Cross-Site Scripting vulnerability. *Note: This issue only affected Firefox for Android. Other operating systems are unaffected. Further details are being temporarily withheld to allow users an opportunity to update.*. This vulnerability affects Firefox < 88.0.1 and Firefox for Android < 88.1.3.

Patch / fix

fixed in 2

Mozilla Firefox 88.0.1
Mozilla Firefox for Android 88.1.3

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-2021-29953 updated 2026-11-06 cvss 6.1

Mozilla: Universal Cross-Site Scripting

Red Hat Enterprise Linux 6 firefox Red Hat Enterprise Linux 7 firefox Red Hat Enterprise Linux 8 firefox
not affected: vulnerable code not present

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

0.65% chance of exploitation in the next 30 days, higher than 51% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD	2.0	4.3	AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

Mozilla Firefox
Mozilla Firefox for Android

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

mozilla.org /security/advisories/mfsa2021-20/
release-notes, vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=1701684
permissions-required, vendor-advisory

Sources

CVE List CVE-2021-29953
NVD CVE-2021-29953

Fencer Vulns 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.

Summary