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Findings

CVE-2026-5731

Memory safety bugs present in Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1.

Published Apr 7, 2026 · updated Jul 15, 2026 · mozilla firefox

Memory safety bugs present in Firefox ESR 115.34.0, 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 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.

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.

  1. Apr 7, 2026 · NIST NVD

    Detected

    Memory safety bugs present in Firefox ESR 115.34.0, 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 115.34.1, Firefox ESR 140.9.1, Thunderbird

  2. Jul 15, 2026 · NIST NVD

    Updated

    Memory safety bugs present in Firefox ESR 115.34.0, 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 115.34.1, Firefox ESR 140.9.1, Thunderbird

Affected

  • cpe mozilla/firefox115.34.0
  • cpe mozilla/firefox140.9.0
  • cpe mozilla/firefox149.0.1
  • cpe mozilla/thunderbird140.9.0
  • cpe mozilla/thunderbird149.0.1

Sources

  • CVE.orgVulnerability recordCVE-2026-5731

    Official CVE identifier

    cve.org
  • NIST NVDVulnerability recordCVE-2026-5731

    Memory safety bugs present in Firefox ESR 115.34.0, 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

    nvd.nist.gov

References

CVE-2026-5731 · ZeroDay Findings