CVE-2026-126135: SMTP and POP3 response injection when using STARTTLS
Noroxi assessment
Priority: Monitor (action score 0/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.18% (FIRST EPSS).
- Fixed version: thunderbird (Debian:12) 1:153.7.0esr-1~deb12u1; thunderbird (Debian:13) 1:153.7.0esr-1~deb13u1.
Low priority for now. Upgrade to thunderbird (Debian:12) 1:153.7.0esr-1~deb12u1; thunderbird (Debian:13) 1:153.7.0esr-1~deb13u1 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
If an attacker was able to perform a man-in-the-middle attack on an SMTP or POP3 server connection using STARTTLS, the attacker could inject server responses before the TLS handshake completed. Thunderbird would process these responses after the handshake, as if they had been received from the server over the encrypted connection. This could be used to make Thunderbird report a different outcome for sending or fetching mail, and to show attacker-controlled text in error messages. The encrypted connection itself was not compromised, and credentials were not exposed. Connections using SSL/TLS instead of STARTTLS were not affected. This vulnerability was fixed in Thunderbird 160 and Thunderbird 153.7.
- Published
- Nov 10, 2026
- Updated
- Nov 10, 2026
- EPSS
- 0.1% · 8th percentile
- CWE
- —
Report tools
Action score
0
Low priority for now.
- CVSS
- 0 / 40 · —
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.1%
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
Is your version affected? Check itNoroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
—
Versions reported by the vendor
Affected version ranges reported by the assigning authority (mozilla). Independent of NVD's CPE analysis and usually ahead of it.
Mozilla Thunderbird
- 153.7 and later · up to and including 153.*not affected · rpm
- 160 and laternot affected · rpm
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:12 | thunderbird | before 1:153.7.0esr-1~deb12u1 | 1:153.7.0esr-1~deb12u1 |
| Debian:13 | thunderbird | before 1:153.7.0esr-1~deb13u1 | 1:153.7.0esr-1~deb13u1 |
| Debian:14 | thunderbird | from 0 | — |
Same product
mozilla: all recordsOther highest-scoring records for the same primary product.
- CVE-2019-11705A flaw in Thunderbird's implementation of iCal causes a stack buffer overflow in icalrecur_add_bydayrules when processing certain email…42Plan
- CVE-2019-11704A flaw in Thunderbird's implementation of iCal causes a heap buffer overflow in icalmemory_strdup_and_dequote when processing certain email…42Plan
- CVE-2019-11703A flaw in Thunderbird's implementation of iCal causes a heap buffer overflow in parser_get_next_char when processing certain email…42Plan
Published before and after this one in the same product
- ← EarlierCVE-2026-126133Nov 10, 2026 · Calendar server credentials could be sent to an HTTP proxy0Monitor
- ← EarlierCVE-2026-126134Nov 10, 2026 · Feed subscriptions could leak NTLM credentials on Windows0Monitor
- Later →CVE-2026-126136Nov 10, 2026 · OAuth2 access token could be sent over an unencrypted connection with Exchange accounts0Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| debian:thunderbird | 1:153.7.0esr-1~deb12u1 · Debian:12 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
- Published
- Fix recorded+2 d
- TodayNov 13, 2026+3 d
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
Not on record for this CVE: patch commit or PR link · variant or chain candidate · public bounty program.
Technical details
No CVSS vector for this record, so attack conditions can't be derived.
Weakness class (CWE)
—
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log (2)
- Fix✗ → ✓
- Exploit maturity— → none
For records you follow, these changes also arrive as notifications. →
References
Show all references (2 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.