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CVE-2021-23959

An XSS bug in internal error pages could have led to various spoofing attacks, including other...

6.1 MediumFix available

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
Required

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
None

Exploit likelihood

0.57%Down 0.1 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used6.1

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

Record
CVE-2021-23959
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CVSS 2.0
4.3 MediumAV:N/AC:M/Au:N/C:N/I:P/A:N
Weakness
CWE-79
Updated
2026-11-02
CVE ListNo score

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

Record
CVE-2021-23959
Updated
2026-11-02
EUVDEUVD-2021-10880No score

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

Record
EUVD-2021-10880
Updated
2026-11-03
GitHub AdvisoriesGHSA-f3g9-x4jw-849gNo score

An XSS bug in internal error pages could have led to various spoofing attacks, including other...

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

Record
GHSA-f3g9-x4jw-849g
Weakness
CWE-79
Updated
2026-11-02
OSVALPINE-CVE-2021-239596.1

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

Record
ALPINE-CVE-2021-23959
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-03
OSVopenSUSE-SU-2024:10600-1No score

MozillaFirefox-92.0-1.2 on GA media

These are all security issues fixed in the MozillaFirefox-92.0-1.2 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:10600-1
Updated
2026-11-02
OSVopenSUSE-SU-2024:14572-1No score

firefox-esr-128.5.1-1.1 on GA media

These are all security issues fixed in the firefox-esr-128.5.1-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:14572-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
firefox
Alpine:v3.13
before 85.0-r0
85.0-r0
firefox
Alpine:v3.14
before 85.0-r0
85.0-r0
firefox
Alpine:v3.15
before 85.0-r0
85.0-r0
firefox
Alpine:v3.16
before 85.0-r0
85.0-r0
firefox
Alpine:v3.17
before 85.0-r0
85.0-r0
firefox
Alpine:v3.18
before 85.0-r0
85.0-r0
firefox
Alpine:v3.19
before 85.0-r0
85.0-r0
firefox
Alpine:v3.20
before 85.0-r0
85.0-r0
firefox
Alpine:v3.21
before 85.0-r0
85.0-r0
firefox
Alpine:v3.22
before 85.0-r0
85.0-r0
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Affected packages
PackageAffectedFixed
firefox
Alpine:v3.23
before 85.0-r0
85.0-r0
librewolf
Alpine:v3.21
before 85.0-r0
85.0-r0
librewolf
Alpine:v3.22
before 85.0-r0
85.0-r0
librewolf
Alpine:v3.23
before 85.0-r0
85.0-r0
librewolf
Alpine:v3.24
before 85.0-r0
85.0-r0
MozillaFirefox
openSUSE:Tumbleweed
From an advisory covering 661 CVEs
before 92.0-1.2
92.0-1.2
firefox-esr
openSUSE:Tumbleweed
From an advisory covering 1860 CVEs
before 128.5.1-1.1
128.5.1-1.1

History

History
RecordedChangedSources
affected, facts
affected, aliases, referencesOSV
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-23959 is a medium vulnerability (CVSS 6.1) in Mozilla Firefox, published February 26, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.57%, the 47th percentile. Fixed in firefox 85.0-r0.

References

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