Vulnerability · CVE-2026-5734
Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1.
Published Apr 7, 2026 · catalog updated Jul 15, 2026 · Memory safety bugs present
Check if you run it
No confirmed exploitation is on record for CVE-2026-5734. EPSS is 0.59%. Act only if a listed version of Memory safety bugs present is installed.
Gaps on this record
- The stored product name is a package slug. The name on this page is taken from the title (Memory safety bugs present).
- No version range is stored. A customer cannot check an installed version against this record.
- No vendor fix or required action is stored. Compare the linked advisory before you change production.
- Severity
- Critical9.8
- Known exploitation
- Not in CISA/VulnCheck KEV
- EPSS
- 0.59%
- Remediation
- Advisory link
- Affected products
- cpe mozilla/firefox · cpe mozilla/thunderbird
Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.
Are you affected?
Enter the version you run. The result uses only the ranges stored on this record.
The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.
- cpe mozilla/firefoxversion unspecified
- cpe mozilla/thunderbirdversion unspecified
How to fix CVE-2026-5734
Recommended remediation
A patch or advisory reference is linked. Open the original publisher for availability by product version.
Official advisories
What to do
Three questions, each answered from this record only. Confirm the vendor advisory before you patch.
Should you patch?
No confirmed exploitation is on record for CVE-2026-5734. EPSS is 0.59%. Act only if a listed version of Memory safety bugs present is installed.
Which versions are affected?
Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.
What should an analyst verify?
CWE-120: Classic Buffer Overflow; CWE-787: Out-of-bounds Write. EPSS 0.59%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.
Code
The project this record applies to. Exploit listings stay in References.
No public source repository is identified for this product.
Timeline
Detection, updates, and resolution for this record.
Apr 7, 2026 · NIST NVD
Detected
Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.
Jul 15, 2026 · NIST NVD
Updated
Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.
Sources
- CVE.orgVulnerability recordCVE-2026-5734
Official CVE identifier
cve.org - FIRST EPSSExploitation probabilityCVE-2026-5734
30-day exploitation probability 0.6%
first.org - NIST NVDVulnerability recordCVE-2026-5734
Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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
nvd.nist.gov
References
Freshness
Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.