CVE-2026-100766 — Information disclosure in the Networking: JAR component

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

1. Identify exposed assets running the affected vendor/product/version combinations (Mozilla Firefox, Mozilla Thunderbird).
2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
4. Exploitation requires user interaction: tighten email/web filtering and warn affected users.
5. Search available logs for exploit probes matching the vulnerability class (info disclosure), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-200 · Exposure of Sensitive Information

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.27%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

• Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
• Look for anomalous data read/export volumes and access to sensitive records.

Timeline

What happened to this CVE, newest first.

• 2026
• SSVC assessment updated
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• Record published
  Oct 13, 2026
• CVSS changed · 4.3
  Oct 13, 2026 · NIST National Vulnerability Database
• Source status changed · → Analyzed
  Oct 13, 2026 · NIST National Vulnerability Database
• Record created in this database
  Oct 13, 2026 · NIST National Vulnerability Database
• CVE published
  Sep 29, 2026 · mozilla

Source activity

Repeated readings are counted rather than listed.

• 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

8 on the record

• www.mozilla.org/security/advisories/mfsa2026-97/
  Vendor Advisory, NIST National Vulnerability Database
• www.mozilla.org/security/advisories/mfsa2026-99/
  Vendor Advisory, NIST National Vulnerability Database
• www.mozilla.org/security/advisories/mfsa2026-102/
  Vendor Advisory, NIST National Vulnerability Database
• www.mozilla.org/security/advisories/mfsa2026-101/
  Vendor Advisory, NIST National Vulnerability Database
• www.mozilla.org/security/advisories/mfsa2026-103/
  Vendor Advisory, NIST National Vulnerability Database
• www.mozilla.org/security/advisories/mfsa2026-100/
  Vendor Advisory, NIST National Vulnerability Database
• www.mozilla.org/security/advisories/mfsa2026-98/
  Vendor Advisory, NIST National Vulnerability Database
• bugzilla.mozilla.org/show_bug.cgi
  Permissions Required, NIST National Vulnerability Database

Elsewhere on this site

Related CVEs (same products)

• Critical CVE-2026-106016 Mitigation bypass in the File Handling component 9d
• Medium CVE-2026-103500 Heap buffer overflow opening large email 15d
• High CVE-2026-100831 Use-after-free in the DOM: UI Events & Focus Handling component 16d
• Critical CVE-2026-100828 Mitigation bypass in the Bookmarks & History component 16d
• Critical CVE-2026-100829 Mitigation bypass in the DOM: Security component 16d
• High CVE-2026-100830 Mitigation bypass in the DOM: Navigation component 16d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

• No fixed version, patch or mitigation documented.
• No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
• No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
• No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-100766 is "Information disclosure in the Networking: JAR component", rated Medium. It affects Firefox (Mozilla); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 4.3 describes technical severity. EPSS 0.25% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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