A transient execution vulnerability, named Floating Point Value Injection (FPVI) allowed an attacker to leak arbitrary memory addresses and…

published 2021-06-24 5y ago modified 2026-06-17 4mo ago also EUVD-2021-16414

cvss: 5.3; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.5%; EPSS 1.5% chance of exploitation in 30 days, percentile 74%
public exploits: 0; none known

A transient execution vulnerability, named Floating Point Value Injection (FPVI) allowed an attacker to leak arbitrary memory addresses and may have also enabled JIT type confusion attacks. (A related vulnerability, Speculative Code Store Bypass (SCSB), did not affect Firefox.). This vulnerability affects Firefox ESR < 78.9 and Firefox < 87.

Patch / fix

fixed in 2 distros 2

Mozilla Firefox ESR 78.9
Mozilla Firefox 87

debian ubuntu

firefox-esr Debian 14, Debian 13, Debian 12 78.9.0esr-1

debian advisories DEBIAN-CVE-2021-29955

firefox Ubuntu 18.04 LTS 87.0+build3-0ubuntu0.18.04.2

ubuntu advisories UBUNTU-CVE-2021-29955

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

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Exploit prediction

1.48% chance of exploitation in the next 30 days, higher than 74% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by	version	score	vector
NVD	3.1	5.3	CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N
NVD	2.0	2.6	AV:N/AC:H/Au:N/C:P/I:N/A:N

Affected products

Mozilla Firefox ESR
Mozilla Firefox

Classification

Weakness

CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component

References

mozilla.org /security/advisories/mfsa2021-10/
release-notes, vendor-advisory
mozilla.org /security/advisories/mfsa2021-11/
release-notes, vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=1692972
permissions-required, vendor-advisory

Sources

CVE List CVE-2021-29955
NVD CVE-2021-29955

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