firefox: Out-of-bounds Read (CVE-2026-92240)

What is affected, what to do

A malicious or compromised IMAP server can trigger an out-of-bounds read in the IMAP response parser by sending an untagged '* ID' response, crashing Thunderbird. The affected parsing path is reachable before authentication.

Update Mozilla Thunderbird to version 140.16.0, Mozilla Thunderbird to version 153.3.0, Mozilla Thunderbird to version 156.0.

Affected

• Mozilla Thunderbird lt *..140.16.0
• Mozilla Thunderbird lt 141.0..153.3.0
• Mozilla Thunderbird lt 154.0..156.0

Fixed in

• Mozilla Thunderbird 140.16.0
• Mozilla Thunderbird 153.3.0
• Mozilla Thunderbird 156.0

Not sure whether and how you are affected? Ask a question about this vulnerability

Metrics

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2

NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

Read in glossary

High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.

CRA

The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

Read in glossary

From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.

ISO/IEC 27001

ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

Read in glossary

Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

A malicious or compromised IMAP server can trigger an out-of-bounds read in the IMAP response parser by sending an untagged '* ID' response, crashing Thunderbird. The affected parsing path is reachable before authentication. This vulnerability was fixed in Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3.

Source: BSI WID Portal

Vendors and products

• Debian Thunderbird
• Mozilla Mozilla Thunderbird

Weakness classes (CWE)

• CWE-125Out-of-bounds Read

  Base

  The product reads data past the end, or before the beginning, of the intended buffer.

  Entry at MITRE CWE-125

References & sources

• bugzilla.mozilla.orgshow_bug.cgi?id=2049342
• mozilla.orgsecurity/advisories/mfsa2026-90
• mozilla.orgsecurity/advisories/mfsa2026-93
• mozilla.orgsecurity/advisories/mfsa2026-94
• mozilla.orgsecurity/advisories/mfsa2026-96
• bugzilla.mozilla.orgshow_bug.cgi?id=2068378
• mozilla.orgsecurity/advisories/mfsa2026-92
• mozilla.orgsecurity/advisories/mfsa2026-95
• bugzilla.mozilla.orgshow_bug.cgi?id=2069113
• bugzilla.mozilla.orgshow_bug.cgi?id=2061393
• bugzilla.mozilla.orgshow_bug.cgi?id=2067971
• bugzilla.mozilla.orgshow_bug.cgi?id=2061295
• bugzilla.mozilla.orgshow_bug.cgi?id=2050150
• bugzilla.mozilla.orgshow_bug.cgi?id=2057990
• bugzilla.mozilla.orgshow_bug.cgi?id=2063814
• bugzilla.mozilla.orgshow_bug.cgi?id=2065346
• bugzilla.mozilla.orgshow_bug.cgi?id=2058068
• mozilla.orgsecurity/advisories/mfsa2026-91
• bugzilla.mozilla.orgshow_bug.cgi?id=2064026
• bugzilla.mozilla.orgshow_bug.cgi?id=2063539

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

1. 24.09.2026Initial analysis by NVDNVD

   Newly listed as affected:

   • Mozilla Thunderbird (before 140.16.0; 141.0 – before 153.3.0; 154.0 – before 156.0)

   New references:

   • https://bugzilla.mozilla.org/show_bug.cgi?id=2069113
   • https://www.mozilla.org/security/advisories/mfsa2026-94/
   • https://www.mozilla.org/security/advisories/mfsa2026-95/
   • https://www.mozilla.org/security/advisories/mfsa2026-96/
   Show 5 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Product configuration	added	—	OR *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* versions up to (excluding) 140.16.0 *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* versions from (including) 141.0 up to (excluding) 153.3.0 *cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* versions from (including) 154.0 up to (excluding) 156.0
   Reference type	added	—	Mozilla Corporation: https://bugzilla.mozilla.org/show_bug.cgi?id=2069113 Types: Permissions Required
   Reference type	added	—	Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-94/ Types: Vendor Advisory
   Reference type	added	—	Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-95/ Types: Vendor Advisory
   Reference type	added	—	Mozilla Corporation: https://www.mozilla.org/security/advisories/mfsa2026-96/ Types: Vendor Advisory

   Source identifier: nvd@nist.gov

2. 22.09.2026Record modifiedCISA ADP

   CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

   CISA assessment (SSVC): exploitation: none known, automatable: yes

   Weakness type: CWE-125

   Show 3 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   CVSS	added	—	AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
   Weakness type (CWE)	added	—	CWE-125
   SSVC assessment	added	—	{"id":"CVE-2026-92240","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-22T15:41:57.658626Z"}

   Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

3. 16.09.2026Record modifiedMozilla

   Description added or changed

   New references:

   • https://www.mozilla.org/security/advisories/mfsa2026-96/
   Show 3 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Description	changed	A malicious or compromised IMAP server can trigger an out-of-bounds read in the IMAP response parser by sending an untagged '* ID' response, crashing Thunderbird. The affected parsing path is reachable before authentication. This vulnerability was fixed in Thunderbird 156 and Thunderbird 140.16.	A malicious or compromised IMAP server can trigger an out-of-bounds read in the IMAP response parser by sending an untagged '* ID' response, crashing Thunderbird. The affected parsing path is reachable before authentication. This vulnerability was fixed in Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3.
   Affected versions (publisher)	added	—	Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/92xxx/CVE-2026-92240.json">CVE-2026-92240</a>
   Reference	added	—	https://www.mozilla.org/security/advisories/mfsa2026-96/

   Source identifier: security@mozilla.org

4. 15.09.2026ReceivedMozilla

   Description added or changed

   New references:

   • https://bugzilla.mozilla.org/show_bug.cgi?id=2069113
   • https://www.mozilla.org/security/advisories/mfsa2026-94/
   • https://www.mozilla.org/security/advisories/mfsa2026-95/
   Show 5 original changes

   Individual changes of this event as published by NVD

   Type	Action	Before	After
   Description	added	—	A malicious or compromised IMAP server can trigger an out-of-bounds read in the IMAP response parser by sending an untagged '* ID' response, crashing Thunderbird. The affected parsing path is reachable before authentication. This vulnerability was fixed in Thunderbird 156 and Thunderbird 140.16.
   Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/92xxx/CVE-2026-92240.json">CVE-2026-92240</a>
   Reference	added	—	https://bugzilla.mozilla.org/show_bug.cgi?id=2069113
   Reference	added	—	https://www.mozilla.org/security/advisories/mfsa2026-94/
   Reference	added	—	https://www.mozilla.org/security/advisories/mfsa2026-95/

   Source identifier: security@mozilla.org