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CVE-2025-1020

Memory safety bugs fixed in Firefox 135 and Thunderbird 135

9.8 CriticalFix available

Memory safety bugs present in Firefox 134 and Thunderbird 134. 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 was fixed in Firefox 135 and Thunderbird 135.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

0.54%Up 0.5 points since Feb 5, 2025
90%50%10%1%

What each source reports

NVD Score used 9.8

Memory safety bugs present in Firefox 134 and Thunderbird 134. 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 was fixed in Firefox 135 and Thunderbird 135.

Record
CVE-2025-1020
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
CVE List 9.8

Memory safety bugs fixed in Firefox 135 and Thunderbird 135

Memory safety bugs present in Firefox 134 and Thunderbird 134. 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 was fixed in Firefox 135 and Thunderbird 135.

Record
CVE-2025-1020
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
EUVDEUVD-2025-1975 9.8

Memory safety bugs present in Firefox 134 and Thunderbird 134. 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 was fixed in Firefox 135 and Thunderbird 135.

Record
EUVD-2025-1975
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
GitHub AdvisoriesGHSA-x7w4-wjh5-78hj 9.8

Memory safety bugs present in Firefox 134 and Thunderbird 134. Some of these bugs showed evidence...

Memory safety bugs present in Firefox 134 and Thunderbird 134. 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 < 135 and Thunderbird < 135.

Record
GHSA-x7w4-wjh5-78hj
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-787
Updated
2026-11-02
OSVUBUNTU-CVE-2025-1020 9.8

Memory safety bugs present in Firefox 134 and Thunderbird 134. 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 was fixed in Firefox 135 and Thunderbird 135.

Record
UBUNTU-CVE-2025-1020
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVopenSUSE-SU-2025:14730-1 No score

MozillaFirefox-135.0-1.1 on GA media

These are all security issues fixed in the MozillaFirefox-135.0-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2025:14730-1
Updated
2026-11-02
OSVopenSUSE-SU-2026:11373-1 No score

firefox-esr-153.0-1.1 on GA media

These are all security issues fixed in the firefox-esr-153.0-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:11373-1
Updated
2026-11-02
OSVUSN-7263-1 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 across domains, or execute arbitrary code. (CVE-2025-1011, CVE-2025-1013, CVE-2025-1014, CVE-2025-1016, CVE-2025-1017, CVE-2025-1018, CVE-2025-1019, CVE-2025-1020)

Ivan Fratric discovered that Firefox did not properly handle XSLT data, leading to a use-after-free vulnerability. An attacker could potentially exploit this issue to cause a denial of service, or execute arbitrary code. (CVE-2025-1009)

Atte Kettunen discovered that Firefox did not properly manage memory in the Custom Highlight API, leading to a use-after-free vulnerability. An attacker could potentially exploit this issue to cause a denial of service, or execute arbitrary code. (CVE-2025-1010)

Nils Bars discovered that Firefox did not properly manage memory during concurrent delazification, leading to a use-after-free vulnerability. An attacker could potentially exploit this issue to cause a denial of service, or execute arbitrary code. (CVE-2025-1012)

Record
USN-7263-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
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 135.0+build2-0ubuntu0.20.04.1, plus listed versions
69.0.3+build1-0ubuntu170.0+build2-0ubuntu170.0+build2-0ubuntu270.0.1+build1-0ubuntu271.0+build2-0ubuntu2
Show 45 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+build1-0ubuntu0.20.04.186.0+build3-0ubuntu0.20.04.186.0.1+build1-0ubuntu0.20.04.187.0+build3-0ubuntu0.20.04.288.0+build2-0ubuntu0.20.04.188.0.1+build1-0ubuntu0.20.04.289.0+build2-0ubuntu0.20.04.289.0.1+build1-0ubuntu0.20.04.189.0.2+build1-0ubuntu0.20.04.190.0+build1-0ubuntu0.20.04.190.0.2+build1-0ubuntu0.20.04.191.0+build2-0ubuntu0.20.04.191.0.1+build1-0ubuntu0.20.04.191.0.2+build1-0ubuntu0.20.04.192.0+build3-0ubuntu0.20.04.1
135.0+build2-0ubuntu0.20.04.1
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
mozjs102
Ubuntu:22.04:LTS
All versions, plus listed versions
102.11.0-0ubuntu0.22.04.1102.12.0-0ubuntu0.22.04.1102.13.0-0ubuntu0.22.04.1102.15.1-0ubuntu0.22.04.1
None known
mozjs78
Ubuntu:22.04:LTS
All versions, plus listed versions
78.13.0-178.15.0-278.15.0-4ubuntu1
None known
mozjs91
Ubuntu:22.04:LTS
All versions, plus listed versions
91.5.1-0ubuntu191.6.0-191.6.0-291.7.0-291.10.0-0ubuntu1
None known
thunderbird
Ubuntu:22.04:LTS
before 1:140.7.1+build1-0ubuntu0.22.04.1, plus listed versions
1:91.1.2+build1-0ubuntu11:91.3.0+build2-0ubuntu11:91.3.1+build1-0ubuntu11:91.3.2+build1-0ubuntu11:91.4.0+build1.1-0ubuntu1
Show 33 moreShow less
1:91.4.0+build2-0ubuntu11:91.5.0+build1-0ubuntu11:91.5.1+build1-0ubuntu11:91.6.1+build1-0ubuntu11:91.7.0+build1-0ubuntu11:91.7.0+build2-0ubuntu11:91.8.0+build2-0ubuntu11:91.9.1+build1-0ubuntu0.22.04.11:91.11.0+build2-0ubuntu0.22.04.11:102.2.2+build1-0ubuntu0.22.04.11:102.4.2+build2-0ubuntu0.22.04.11:102.7.1+build2-0ubuntu0.22.04.11:102.8.0+build2-0ubuntu0.22.04.11:102.9.0+build1-0ubuntu0.22.04.11:102.10.0+build2-0ubuntu0.22.04.11:102.11.0+build1-0ubuntu0.22.04.11:102.13.0+build1-0ubuntu0.22.04.11:102.15.0+build1-0ubuntu0.22.04.11:102.15.1+build1-0ubuntu0.22.04.11:115.3.1+build1-0ubuntu0.22.04.21:115.4.1+build1-0ubuntu0.22.04.11:115.5.0+build1-0ubuntu0.22.04.11:115.6.0+build2-0ubuntu0.22.04.11:115.8.1+build1-0ubuntu0.22.04.11:115.9.0+build1-0ubuntu0.22.04.11:115.10.1+build1-0ubuntu0.22.04.11:115.11.0+build2-0ubuntu0.22.04.11:115.12.0+build3-0ubuntu0.22.04.11:115.13.0+build5-0ubuntu0.22.04.11:115.15.0+build1-0ubuntu0.22.04.11:115.16.0+build2-0ubuntu0.22.04.11:115.18.0+build1-0ubuntu0.22.04.11:128.12.0+build1-0ubuntu0.22.04.1
1:140.7.1+build1-0ubuntu0.22.04.1
mozjs102
Ubuntu:24.04:LTS
All versions, plus listed versions
102.15.1-1102.15.1-3ubuntu2
None known
Show 4 moreShow less
Affected packages
PackageAffectedFixed
mozjs115
Ubuntu:24.04:LTS
All versions, plus listed versions
115.3.0-0ubuntu1115.4.0-2115.5.0-1115.6.0-1115.7.0-4
Show 4 moreShow less
115.8.0-1115.9.0-1115.9.0-1build1115.10.0-1
None known
firefox
Ubuntu:20.04:LTS
From an advisory covering 11 CVEs
before 135.0+build2-0ubuntu0.20.04.1, plus listed versions
69.0.3+build1-0ubuntu170.0+build2-0ubuntu170.0+build2-0ubuntu270.0.1+build1-0ubuntu271.0+build2-0ubuntu2
Show 45 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+build1-0ubuntu0.20.04.186.0+build3-0ubuntu0.20.04.186.0.1+build1-0ubuntu0.20.04.187.0+build3-0ubuntu0.20.04.288.0+build2-0ubuntu0.20.04.188.0.1+build1-0ubuntu0.20.04.289.0+build2-0ubuntu0.20.04.289.0.1+build1-0ubuntu0.20.04.189.0.2+build1-0ubuntu0.20.04.190.0+build1-0ubuntu0.20.04.190.0.2+build1-0ubuntu0.20.04.191.0+build2-0ubuntu0.20.04.191.0.1+build1-0ubuntu0.20.04.191.0.2+build1-0ubuntu0.20.04.192.0+build3-0ubuntu0.20.04.1
135.0+build2-0ubuntu0.20.04.1
MozillaFirefox
openSUSE:Tumbleweed
From an advisory covering 11 CVEs
before 135.0-1.1
135.0-1.1
firefox-esr
openSUSE:Tumbleweed
From an advisory covering 228 CVEs
before 153.0-1.1
153.0-1.1

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

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

In short

CVE-2025-1020 is a critical vulnerability (CVSS 9.8) in Mozilla Firefox, published February 4, 2025. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.54%, the 45th percentile. Fixed in firefox 135.0+build2-0ubuntu0.20.04.1.

References

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Left out here: 154 versions and 57 references. The JSON record has them.

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