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CVE-2021-23979

Mozilla developers reported memory safety bugs present in Firefox 85. Some of these bugs showed...

8.8 HighFix available

CVE-2021-23979 is a high vulnerability (CVSS 8.8) 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 0.92%, the 60th percentile. Fixed in firefox 87.0-r0.

Mozilla developers reported memory safety bugs present in Firefox 85. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 86.

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
High
Integrity
High
Availability
High

Exploit likelihood

0.92%Up 0.4 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used 8.8

Mozilla developers reported memory safety bugs present in Firefox 85. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 86.

Record
CVE-2021-23979
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS 2.0
6.8 MediumAV:N/AC:M/Au:N/C:P/I:P/A:P
Weakness
CWE-787
Updated
2026-11-02
CVE List No score

Mozilla developers reported memory safety bugs present in Firefox 85. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 86.

Record
CVE-2021-23979
Updated
2026-11-02
EUVDEUVD-2021-10900 No score

Mozilla developers reported memory safety bugs present in Firefox 85. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 86.

Record
EUVD-2021-10900
Updated
2026-11-03
GitHub AdvisoriesGHSA-h2wp-qp38-rjj4 8.8

Mozilla developers reported memory safety bugs present in Firefox 85. Some of these bugs showed...

Mozilla developers reported memory safety bugs present in Firefox 85. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 86.

Record
GHSA-h2wp-qp38-rjj4
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Weakness
CWE-119, CWE-787
Updated
2026-11-02
OSVALPINE-CVE-2021-23979 8.8

Mozilla developers reported memory safety bugs present in Firefox 85. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 86.

Record
ALPINE-CVE-2021-23979
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Updated
2026-11-03
OSVOESA-2023-1673 10.0

firefox security update

Mozilla Firefox is a standalone web browser, designed for standards compliance and performance. Its functionality can be enhanced via a plethora of extensions.

Mozilla Firefox is an open-source web browser, designed for standards compliance, performance and portability.

Security Fix(es):

Mozilla developers reported memory safety bugs present in Firefox for Android 79. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 80, Firefox ESR < 78.2, Thunderbird < 78.2, and Firefox for Android < 80.(CVE-2020-15670)

Mozilla developers reported memory safety bugs present in Firefox 80 and Firefox ESR 78.2. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 81, Thunderbird < 78.3, and Firefox ESR < 78.3.(CVE-2020-15673)

Mozilla developers reported memory safety bugs present in Firefox 80. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 81.(CVE-2020-15674)

When processing surfaces, the lifetime may outlive a persistent buffer leading to memory corruption and a potentially exploitable crash. This vulnerability affects Firefox < 81.(CVE-2020-15675)

If a valid external protocol handler was referenced in an image tag, the resulting broken image size could be distinguished from a broken image size of a non-existent protocol handler. This allowed an attacker to successfully probe whether an external protocol handler was registered. This vulnerability affects Firefox < 82.(CVE-2020-15680)

When multiple WASM threads had a reference to a module, and were looking up exported functions, one WASM thread could have overwritten another's entry in a shared stub table, resulting in a potentially exploitable crash. This vulnerability affects Firefox < 82.(CVE-2020-15681)

When a link to an external protocol was clicked, a prompt was presented that allowed the user to choose what application to open it in. An attacker could induce that prompt to be associated with an origin they didn't control, resulting in a spoofing attack. This was fixed by changing external protocol prompts to be tab-modal while also ensuring they could not be incorrectly associated with a different origin. This vulnerability affects Firefox < 82.(CVE-2020-15682)

Mozilla developers and community members reported memory safety bugs present in Firefox 81 and Firefox ESR 78.3. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox ESR < 78.4, Firefox < 82, and Thunderbird < 78.4.(CVE-2020-15683)

Mozilla developers reported memory safety bugs present in Firefox 81. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 82.(CVE-2020-15684)

Side-channel information leakage in graphics in Google Chrome prior to 87.0.4280.66 allowed a remote attacker to leak cross-origin data via a crafted HTML page.(CVE-2020-16012)

Use after free in WebRTC in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to potentially exploit heap corruption via a crafted SCTP packet.(CVE-2020-16044)

In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable use-after-free condition. This vulnerability affects Firefox < 82.0.3, Firefox ESR < 78.4.1, and Thunderbird < 78.4.2.(CVE-2020-26950)

(CVE-2020-26951)

(CVE-2020-26953) …

Record
OESA-2023-1673
CVSS 3.1
10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Updated
2026-11-02
Show 5 moreShow less
OSVOESA-2023-1674 10.0

firefox security update

Mozilla Firefox is a standalone web browser, designed for standards compliance and performance. Its functionality can be enhanced via a plethora of extensions.

Mozilla Firefox is an open-source web browser, designed for standards compliance, performance and portability.

Security Fix(es):

Mozilla developers reported memory safety bugs present in Firefox for Android 79. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 80, Firefox ESR < 78.2, Thunderbird < 78.2, and Firefox for Android < 80.(CVE-2020-15670)

Mozilla developers reported memory safety bugs present in Firefox 80 and Firefox ESR 78.2. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 81, Thunderbird < 78.3, and Firefox ESR < 78.3.(CVE-2020-15673)

Mozilla developers reported memory safety bugs present in Firefox 80. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 81.(CVE-2020-15674)

When processing surfaces, the lifetime may outlive a persistent buffer leading to memory corruption and a potentially exploitable crash. This vulnerability affects Firefox < 81.(CVE-2020-15675)

If a valid external protocol handler was referenced in an image tag, the resulting broken image size could be distinguished from a broken image size of a non-existent protocol handler. This allowed an attacker to successfully probe whether an external protocol handler was registered. This vulnerability affects Firefox < 82.(CVE-2020-15680)

When multiple WASM threads had a reference to a module, and were looking up exported functions, one WASM thread could have overwritten another's entry in a shared stub table, resulting in a potentially exploitable crash. This vulnerability affects Firefox < 82.(CVE-2020-15681)

When a link to an external protocol was clicked, a prompt was presented that allowed the user to choose what application to open it in. An attacker could induce that prompt to be associated with an origin they didn't control, resulting in a spoofing attack. This was fixed by changing external protocol prompts to be tab-modal while also ensuring they could not be incorrectly associated with a different origin. This vulnerability affects Firefox < 82.(CVE-2020-15682)

Mozilla developers and community members reported memory safety bugs present in Firefox 81 and Firefox ESR 78.3. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox ESR < 78.4, Firefox < 82, and Thunderbird < 78.4.(CVE-2020-15683)

Mozilla developers reported memory safety bugs present in Firefox 81. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 82.(CVE-2020-15684)

Side-channel information leakage in graphics in Google Chrome prior to 87.0.4280.66 allowed a remote attacker to leak cross-origin data via a crafted HTML page.(CVE-2020-16012)

Use after free in WebRTC in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to potentially exploit heap corruption via a crafted SCTP packet.(CVE-2020-16044)

In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable use-after-free condition. This vulnerability affects Firefox < 82.0.3, Firefox ESR < 78.4.1, and Thunderbird < 78.4.2.(CVE-2020-26950)

(CVE-2020-26951)

(CVE-2020-26953) …

Record
OESA-2023-1674
CVSS 3.1
10.0 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2021-23979 8.8

Mozilla developers reported memory safety bugs present in Firefox 85. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 86.

Record
UBUNTU-CVE-2021-23979
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVopenSUSE-SU-2024:10600-1 No 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-2024:14572-1 No 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
OSVUSN-4756-1 No score

firefox vulnerabilities

Multiple security issues were discovered in Firefox. If a user were tricked into opening a specially crafted website, an attacker could potentially exploit these to cause a denial of service, obtain sensitive information, conduct cross-site scripting (XSS) attacks, bypass HTTP auth phishing warnings, or execute arbitrary code.

Record
USN-4756-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
firefox
Alpine:v3.13
before 87.0-r0
87.0-r0
firefox
Alpine:v3.14
before 87.0-r0
87.0-r0
firefox
Alpine:v3.15
before 87.0-r0
87.0-r0
firefox
Alpine:v3.16
before 87.0-r0
87.0-r0
firefox
Alpine:v3.17
before 87.0-r0
87.0-r0
firefox
Alpine:v3.18
before 87.0-r0
87.0-r0
firefox
Alpine:v3.19
before 87.0-r0
87.0-r0
firefox
Alpine:v3.20
before 87.0-r0
87.0-r0
firefox
Alpine:v3.21
before 87.0-r0
87.0-r0
firefox
Alpine:v3.22
before 87.0-r0
87.0-r0
Show 17 moreShow less
Affected packages
PackageAffectedFixed
firefox
Alpine:v3.23
before 87.0-r0
87.0-r0
librewolf
Alpine:v3.21
before 87.0-r0
87.0-r0
librewolf
Alpine:v3.22
before 87.0-r0
87.0-r0
librewolf
Alpine:v3.23
before 87.0-r0
87.0-r0
librewolf
Alpine:v3.24
before 87.0-r0
87.0-r0
firefox
openEuler:22.03-LTS
before 102.14.0-1.oe2203
102.14.0-1.oe2203
firefox
openEuler:22.03-LTS-SP1
before 102.14.0-1.oe2203sp1
102.14.0-1.oe2203sp1
firefox
Ubuntu:16.04:LTS
before 86.0+build3-0ubuntu0.16.04.1, plus listed versions
41.0.2+build2-0ubuntu142.0+build2-0ubuntu144.0+build3-0ubuntu244.0.1+build1-0ubuntu144.0.2+build1-0ubuntu1
Show 45 moreShow less
45.0+build2-0ubuntu145.0.1+build1-0ubuntu145.0.2+build1-0ubuntu146.0+build5-0ubuntu0.16.04.246.0.1+build1-0ubuntu0.16.04.247.0+build3-0ubuntu0.16.04.148.0+build2-0ubuntu0.16.04.149.0+build4-0ubuntu0.16.04.149.0.2+build2-0ubuntu0.16.04.250.0+build2-0ubuntu0.16.04.250.0.2+build1-0ubuntu0.16.04.150.1.0+build2-0ubuntu0.16.04.151.0.1+build2-0ubuntu0.16.04.151.0.1+build2-0ubuntu0.16.04.252.0+build2-0ubuntu0.16.04.152.0.1+build2-0ubuntu0.16.04.152.0.2+build1-0ubuntu0.16.04.153.0+build6-0ubuntu0.16.04.153.0.2+build1-0ubuntu0.16.04.253.0.3+build1-0ubuntu0.16.04.254.0+build3-0ubuntu0.16.04.155.0.1+build2-0ubuntu0.16.04.255.0.2+build1-0ubuntu0.16.04.156.0+build6-0ubuntu0.16.04.156.0+build6-0ubuntu0.16.04.257.0+build4-0ubuntu0.16.04.557.0+build4-0ubuntu0.16.04.657.0.1+build2-0ubuntu0.16.04.157.0.3+build1-0ubuntu0.16.04.157.0.4+build1-0ubuntu0.16.04.158.0+build6-0ubuntu0.16.04.158.0.1+build1-0ubuntu0.16.04.158.0.2+build1-0ubuntu0.16.04.159.0+build5-0ubuntu0.16.04.159.0.1+build1-0ubuntu0.16.04.159.0.2+build1-0ubuntu0.16.04.159.0.2+build1-0ubuntu0.16.04.360.0+build2-0ubuntu0.16.04.160.0.1+build2-0ubuntu0.16.04.160.0.2+build1-0ubuntu0.16.04.161.0+build3-0ubuntu0.16.04.261.0.1+build1-0ubuntu0.16.04.162.0+build2-0ubuntu0.16.04.362.0+build2-0ubuntu0.16.04.462.0+build2-0ubuntu0.16.04.5
86.0+build3-0ubuntu0.16.04.1
firefox
Ubuntu:18.04:LTS
before 86.0+build3-0ubuntu0.18.04.1, plus listed versions
56.0+build6-0ubuntu157.0.1+build2-0ubuntu159.0.1+build1-0ubuntu159.0.2+build1-0ubuntu160.0+build2-0ubuntu1
Show 45 moreShow less
60.0.1+build2-0ubuntu0.18.04.160.0.2+build1-0ubuntu0.18.04.161.0+build3-0ubuntu0.18.04.161.0.1+build1-0ubuntu0.18.04.162.0+build2-0ubuntu0.18.04.362.0+build2-0ubuntu0.18.04.462.0+build2-0ubuntu0.18.04.562.0.3+build1-0ubuntu0.18.04.163.0+build2-0ubuntu0.18.04.263.0.3+build1-0ubuntu0.18.04.164.0+build3-0ubuntu0.18.04.165.0+build2-0ubuntu0.18.04.165.0.1+build2-0ubuntu0.18.04.166.0+build3-0ubuntu0.18.04.166.0.1+build1-0ubuntu0.18.04.166.0.2+build1-0ubuntu0.18.04.166.0.3+build1-0ubuntu0.18.04.166.0.4+build3-0ubuntu0.18.04.166.0.5+build1-0ubuntu0.18.04.167.0+build2-0ubuntu0.18.04.167.0.1+build1-0ubuntu0.18.04.167.0.2+build2-0ubuntu0.18.04.167.0.3+build1-0ubuntu0.18.04.167.0.4+build1-0ubuntu0.18.04.168.0+build3-0ubuntu0.18.04.168.0.1+build1-0ubuntu0.18.04.168.0.2+build1-0ubuntu0.18.04.169.0+build2-0ubuntu0.18.04.169.0.1+build1-0ubuntu0.18.04.169.0.2+build1-0ubuntu0.18.04.170.0+build2-0ubuntu0.18.04.170.0.1+build1-0ubuntu0.18.04.171.0+build5-0ubuntu0.18.04.172.0.1+build1-0ubuntu0.18.04.172.0.2+build1-0ubuntu0.18.04.173.0+build3-0ubuntu0.18.04.173.0.1+build1-0ubuntu0.18.04.174.0+build3-0ubuntu0.18.04.174.0.1+build1-0ubuntu0.18.04.175.0+build3-0ubuntu0.18.04.176.0+build2-0ubuntu0.18.04.176.0.1+build1-0ubuntu0.18.04.177.0.1+build1-0ubuntu0.18.04.178.0.1+build1-0ubuntu0.18.04.178.0.2+build2-0ubuntu0.18.04.1
86.0+build3-0ubuntu0.18.04.1
mozjs52
Ubuntu:18.04:LTS
All versions, plus listed versions
52.3.1-0ubuntu352.3.1-7fakesync152.8.1-0ubuntu0.18.04.152.9.1-0ubuntu0.18.04.1
None known
mozjs38
Ubuntu:18.04:LTS
All versions, plus listed versions
38.8.0~repack1-0ubuntu138.8.0~repack1-0ubuntu338.8.0~repack1-0ubuntu4
None known
firefox
Ubuntu:20.04:LTS
before 86.0+build3-0ubuntu0.20.04.1, plus listed versions
69.0.3+build1-0ubuntu170.0+build2-0ubuntu170.0+build2-0ubuntu270.0.1+build1-0ubuntu271.0+build2-0ubuntu2
Show 31 moreShow less
71.0+build5-0ubuntu172.0.1+build1-0ubuntu172.0.2+build1-0ubuntu173.0+build1-0ubuntu173.0+build2-0ubuntu173.0+build3-0ubuntu173.0.1+build1-0ubuntu174.0+build1-0ubuntu174.0+build2-0ubuntu174.0+build2-0ubuntu274.0+build3-0ubuntu175.0+build3-0ubuntu176.0+build2-0ubuntu0.20.04.176.0.1+build1-0ubuntu0.20.04.177.0.1+build1-0ubuntu0.20.04.178.0.1+build1-0ubuntu0.20.04.178.0.2+build2-0ubuntu0.20.04.179.0+build1-0ubuntu0.20.04.180.0+build2-0ubuntu0.20.04.180.0.1+build1-0ubuntu0.20.04.181.0+build2-0ubuntu0.20.04.181.0.2+build1-0ubuntu0.20.04.182.0+build2-0ubuntu0.20.04.182.0.2+build1-0ubuntu0.20.04.182.0.3+build1-0ubuntu0.20.04.183.0+build2-0ubuntu0.20.04.184.0+build3-0ubuntu0.20.04.184.0.1+build1-0ubuntu0.20.04.184.0.2+build1-0ubuntu0.20.04.185.0+build1-0ubuntu0.20.04.185.0.1+build1-0ubuntu0.20.04.1
86.0+build3-0ubuntu0.20.04.1
mozjs68
Ubuntu:20.04:LTS
All versions, plus listed versions
68.5.0-1~fakesync68.5.0-2~fakesync68.6.0-168.6.0-1ubuntu1
None known
mozjs52
Ubuntu:20.04:LTS
All versions, plus listed versions
52.9.1-1build152.9.1-1ubuntu3
None known
mozjs78
Ubuntu:22.04:LTS
All versions, plus listed versions
78.13.0-178.15.0-278.15.0-4ubuntu1
None known
MozillaFirefox
openSUSE:Tumbleweed
before 92.0-1.2
92.0-1.2
firefox-esr
openSUSE:Tumbleweed
before 128.5.1-1.1
128.5.1-1.1

History

History
WhenChangedSources
2026-11-03affected, aliases, referencesOSV
2026-11-03aliasesEUVD
2026-11-02createdCVE List, GitHub Advisories, NVD, OSV

References

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Left out here: 65 versions, 1,969 references and the rest of 2 source descriptions. The JSON record has them.

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