CVE-2026-113866: Account password sent unencrypted during Exchange account setup
Vulnerability summary
CVE-2026-113866 is a medium (CVSS 5.9) Unprotected Transport of Credentials vulnerability in thunderbird. EPSS estimates a 0.36% chance of exploitation in the next 30 days, higher than 30.3% of scored vulnerabilities.
Not severe (CVSS 5.9, network access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 1 · Related 1Timeline
- 20-10-2026PublishedVulnerability first disclosed.
- 20-10-2026Last modifiedVulnerability information updated.
Description
When setting up an account, Thunderbird's Exchange AutoDiscover lookup also queried the domain's AutoDiscover service over plain HTTP. Due to a bug, that unencrypted request included the credentials the user had entered, allowing a network attacker to obtain the user's password. This vulnerability was fixed in Thunderbird 158.0.1 and Thunderbird 153.5.1.
CVSS metrics
4 scores · 4 sources · 1 version- NVDNIST5.9MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- OSV · DebianEcosystem advisory · calculated5.9MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- OSV · UbuntuEcosystem advisory · calculated5.9MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS trend
Probability
0.36%
Chance of exploitation in the next 30 days
Percentile
30%
Versus all other CVEs
30-day change
Change unavailable
Change unavailable
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 causeAffected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Debian1 product
- thunderbirdAll versions (No fix recorded) | < 1:153.5.1esr-1~deb12u1 | < 1:153.5.1esr-1~deb13u1
Ubuntu1 product
- thunderbirdAll versions (No fix recorded)
2 vendors · 2 products
