Memory disclosure or crash via negative IMAP length
Published Mar 24, 2026 · Updated Mar 24, 2026
Out-of-bounds read in Thunderbird before 149 and Thunderbird ESR before 140.9 allows remote attackers to leak memory or crash the client. The IMAP string parser accepts a negative length from a server response and reads past the associated buffer instead of rejecting the malformed value. Exploitation requires a malicious mail server or a compromised server connection; the bounded consequences are sensitive-memory disclosure and a Thunderbird crash.
Summary
What happened
Out-of-bounds read in Thunderbird before 149 and Thunderbird ESR before 140.9 allows remote attackers to leak memory or crash the client. The IMAP string parser accepts a negative length from a server response and reads past the associated buffer instead of rejecting the malformed value. Exploitation requires a malicious mail server or a compromised server connection; the bounded consequences are sensitive-memory disclosure and a Thunderbird crash.
The record
- CVE
- CVE-2026-4371
- Published
- Mar 24, 2026
- Updated
- Mar 24, 2026
- Vendor
- Mozilla
- Product
- Thunderbird
- Classifications
- CWE-126, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 24, 2026CVE publishedPublication date reported by the CVE source.
- Mar 24, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=unspecified <140.9
- Affected versionversion=unspecified <149
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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