CVE-2026-110247: Integer overflow in libmime buffer growth could lead to heap corruption

Published Oct 13, 2026
·
Updated

Several buffer-growth sites in libmime performed size arithmetic in 32-bit types without overflow checks. On a sufficiently large message the growth guard could fail open, or the buffer could be reallocated smaller than required, and a subsequent memcpy would then write attacker-controlled data across adjacent heap allocations. This vulnerability was fixed in Thunderbird 158 and Thunderbird 153.6.

Affected Software

8 affected componentsFixes available
Mozilla Thunderbird<158
Mozilla Thunderbird<153.6
153.6
ubuntu/thunderbird*
ubuntu/thunderbird*
ubuntu/thunderbird*
ubuntu/thunderbird*
debian/thunderbird
1:140.12.0esr-1~deb12u11:153.6.0esr-1~deb12u11:140.12.0esr-1~deb13u11:153.5.1esr-1~deb13u21:153.5.0esr-11:153.6.0esr-1
Mozilla Thunderbird<158
158

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 153.6
  2. Upgrade

    Upgrade debian/thunderbird to a version that resolves this vulnerability.

    Fixed in 1:140.12.0esr-1~deb12u1Fixed in 1:153.6.0esr-1~deb12u1Fixed in 1:140.12.0esr-1~deb13u1Fixed in 1:153.5.1esr-1~deb13u2Fixed in 1:153.5.0esr-1Fixed in 1:153.6.0esr-1
  3. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Fixed in 158
  4. Upgrade

    Upgrade Thunderbird to a version that resolves this vulnerability.

    Fixed in 158
  5. Upgrade

    Upgrade Thunderbird to a version that resolves this vulnerability.

    Fixed in 153.6

Event History

Oct 13, 2026
CVE Published
via Mozilla·12:00 AM
Data Sourced
via Mozilla·12:00 AM
DescriptionSeverityAffected Software
Data Sourced
via Ubuntu·12:00 AM
RemedyDescriptionSeverityAffected Software
CVE Published
via MITRE·06:08 PM
Data Sourced
via MITRE·06:08 PM
Description
Data Sourced
via OSV·07:18 PM
DescriptionSeverityAffected Software
Data Sourced
via NVD·07:18 PM
DescriptionSeverityWeakness

Parent advisories

This vulnerability appears in the following advisories.

Peer vulnerabilities

Found alongside the following vulnerabilities.

Frequently Asked Questions

1

Which Thunderbird versions need remediation?

The issue was fixed in Thunderbird 158. The provided information does not identify the first affected version, so deployments should verify whether they are running a release earlier than 158.

2

What would an attacker need to exploit this issue?

An attacker would need to cause Thunderbird's libmime component to process a sufficiently large message containing attacker-controlled data. The vulnerable buffer-growth arithmetic can result in a smaller-than-required allocation followed by a memcpy that overwrites adjacent heap memory.

Company

Resources

Contact

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