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JIT miscompilation in Firefox DOM: Core & HTML

IdentifiersCVE-2026-12299CWE-682

CVE-2026-12299 is a JIT miscompilation vulnerability in Mozilla's DOM: Core & HTML component affecting Firefox and related Mozilla products. The provided content describes the issue as a JIT miscompilation bug that can result in unpredictable execution behavior when processing specially crafted web content. While the vulnerable function is not identified in the available material, the flaw is in JIT-compiled logic associated with DOM/HTML handling rather than a conventional memory-management bug explicitly tied to a named function. Mozilla fixed the issue in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.

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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.

The specific downstream impact of this individual CVE is not fully described in the provided content. Based on the available advisories, successful exploitation could cause unpredictable execution behavior in the browser and may contribute to broader security consequences seen in the Mozilla advisory set, including potential arbitrary code execution in severe cases. However, for CVE-2026-12299 specifically, the available information does not conclusively state a standalone demonstrated impact beyond security-relevant misexecution caused by JIT miscompilation.

Mitigation

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

No specific vendor workaround or temporary mitigation is provided in the supplied content. The primary mitigation is prompt patching. Until updates are fully deployed, organizations can reduce exposure by limiting access to untrusted web content, enforcing least privilege for browser users, and applying browser and host exploit-protection controls, but these are general risk-reduction measures rather than a vulnerability-specific fix.

Remediation

Patch, then assume compromise.

Upgrade affected Mozilla products to fixed versions. The provided content states that the vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12. Debian users should apply the corresponding firefox-esr package update referenced in the advisory stream 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
MozillaThunderbirdapplication

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

ACTIVITY FEED

Recent activity

7 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

7 SOURCESView more in app
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 activity

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

EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2026-12299
NVD
nvd.nist.gov/vuln/detail/CVE-2026-12299
MITRE CWE · CWE-682
cwe.mitre.org
Vendor Advisory
mozilla.org/security/advisories/mfsa2026-57
Vendor Advisory
mozilla.org/security/advisories/mfsa2026-58
Vendor Advisory
mozilla.org/security/advisories/mfsa2026-59
Vendor Advisory
mozilla.org/security/advisories/mfsa2026-60
Vendor Advisory
mozilla.org/security/advisories/mfsa2026-61
Permissions Required
bugzilla.mozilla.org/show_bug.cgi?id=2043139