CVE-2026-4371: Out of bounds read in IMAP parsing
Vulnerability summary
CVE-2026-4371 is a high (CVSS 7.4) Buffer Over-read vulnerability in mozilla thunderbird. EPSS estimates a 0.37% chance of exploitation in the next 30 days, higher than 30.5% of scored vulnerabilities.
Severe, CVSS 7.4 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 0% (FIRST, 03-11-2026)
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 16 · Related 2Timeline
- 24-03-2026PublishedVulnerability first disclosed.
- 15-07-2026Last modifiedVulnerability information updated.
Description
A malicious mail server could send malformed strings with negative lengths, causing the parser to read memory outside the buffer. If a mail server or connection to a mail server were compromised, an attacker could cause the parser to malfunction, potentially crashing Thunderbird or leaking sensitive data. This vulnerability was fixed in Thunderbird 149 and Thunderbird 140.9.
CVSS metrics
4 scores · 4 sources · 1 version- OSV · UbuntuEcosystem advisory · calculated8.2HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:HDiffers
- OSV · DebianEcosystem advisory · calculated7.4HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
- NVDNIST7.4HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
EPSS trend
Probability
0.37%
Chance of exploitation in the next 30 days
Percentile
31%
Versus all other CVEs
30-day change
Decrease -0.27 pp
From 0.64% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-126Buffer Over-readThe product reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.
- CWE-130Improper Handling of Length Parameter InconsistencyThe product parses a formatted message or structure, but it does not handle or incorrectly handles a length field that is inconsistent with the actual length of the associated data.
Affected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Ubuntu8 products
- mozjs102All versions (No fix recorded)
- mozjs115All versions (No fix recorded)
- mozjs38All versions (No fix recorded)
- mozjs52All versions (No fix recorded)
- mozjs68All versions (No fix recorded)
Debian1 product
- thunderbird< 1:140.9.0esr-1~deb12u1 | < 1:140.9.0esr-1~deb13u1 | < 1:140.9.0esr-1
Mozilla1 product
- thunderbird< 140.9.0 | < 149.0
3 vendors · 10 products
