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High

Memory safety bug in Mozilla Firefox and Thunderbird

IdentifiersCVE-2026-12305CWE-119· Improper Restriction of Operations…

CVE-2026-12305 is a memory safety vulnerability affecting Mozilla Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR. The available advisory text only identifies it generically as a "memory safety bug" and does not provide the specific vulnerable component, function, or root-cause details. Mozilla indicates the issue was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12. As with similar Mozilla memory safety issues, the flaw may permit memory corruption under certain conditions during processing of attacker-controlled content.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation could cause memory corruption and application instability, and may potentially lead to arbitrary code execution. Broader Mozilla and downstream advisories for the affected release train also note possible impacts including denial of service via crash; however, for this specific CVE, the available information supports memory corruption with possible code execution as the primary impact.

Mitigation

If you can’t patch tonight, do this now.

No vendor-supplied workaround or temporary mitigation is documented in the provided content. Until patching is completed, reduce exposure by limiting access to untrusted web content and email content, enforcing least privilege, avoiding administrative execution contexts, and using exploit-mitigation and endpoint protection controls where available.

Remediation

Patch, then assume compromise.

Upgrade affected products to the fixed versions provided by Mozilla: Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird ESR 140.12, or later versions incorporating the fix. Downstream distributions should apply the corresponding vendor-packaged updates, such as Debian firefox-esr 140.12.0esr-1~deb13u1 where applicable.
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType
MozillaFirefoxapplication
MozillaFirefox Esrapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

7 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

7 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.
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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity2

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2026-12305
NVD
nvd.nist.gov/vuln/detail/CVE-2026-12305
MITRE CWE · CWE-119
Improper Restriction of Operations within the…
bugzilla.mozilla.org
bugzilla.mozilla.org/show_bug.cgi?id=2037290
mozilla.org
mozilla.org/security/advisories/mfsa2026-57
mozilla.org
mozilla.org/security/advisories/mfsa2026-58
mozilla.org
mozilla.org/security/advisories/mfsa2026-60
mozilla.org
mozilla.org/security/advisories/mfsa2026-61