CVE-2021-29958

Name: CVE-2021-29958
Creator: NVD / NIST
Published: 2021-06-24T14:15:10.143+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.3/10EPSS 0.67%

Last modified Jun 17, 2026

CVE-2021-29958 is a medium-severity vulnerability rated 4.3/10 on the CVSS scale. When a download was initiated, the client did not check whether it was in normal or private browsing mode, which led to private mode cookies being shared in normal browsing mode. This vulnerability affects Firefox for iOS < 34.. EPSS estimates a 0.67% chance of exploitation in the next 30 days.

Description

When a download was initiated, the client did not check whether it was in normal or private browsing mode, which led to private mode cookies being shared in normal browsing mode. This vulnerability affects Firefox for iOS < 34.

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

EPSS Probability

0.67%

47.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-862

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 34.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1670127Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-25/Release Notes, Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1670127Permissions Required, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-25/Release Notes, Vendor Advisory

Timeline

Published: Jun 24, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-29958?

How severe is CVE-2021-29958?

CVE-2021-29958 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.67% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29958?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-29958?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST