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NVD / CVE Program· CNA mozilla

CVE-2026-0818: CSS-based exfiltration of the content from partially encrypted emails when allowing remote content

Noroxi assessment

Priority: Monitor (action score 17/100)

  • 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: 0.17% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
  • Fixed version: thunderbird (Debian:11) 1:140.7.1esr-1~deb11u1; thunderbird (Debian:12) 1:140.7.1esr-1~deb12u1; thunderbird (Debian:13) 1:140.7.1esr-1~deb13u1.

Low priority for now. Upgrade to thunderbird (Debian:11) 1:140.7.1esr-1~deb11u1; thunderbird (Debian:12) 1:140.7.1esr-1~deb12u1; thunderbird (Debian:13) 1:140.7.1esr-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

When a user explicitly requested Thunderbird to decrypt an inline OpenPGP message that was embedded in a text section of an email that was formatted and styled with HTML and CSS, then the decrypted contents were rendered in a context in which the CSS styles from the outer messages were active. If the user had additionally allowed loading of the remote content referenced by the outer email message, and the email was crafted by the sender using a combination of CSS rules and fonts and animations, then it was possible to extract the secret contents of the email. This vulnerability was fixed in Thunderbird 147.0.1 and Thunderbird 140.7.1.

MediumCVSS 4.3 · v3.1—No exploit Fix available
Published
Jan 28, 2026
Updated
Jun 17, 2026
EPSS
0.1% · 7th percentile

Report tools

JSON

Action score

17

Monitor

Low priority for now.

CVSS
17 / 40 · 4.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

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.

Follow CVE-2026-0818

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi 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.

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Affected 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.

VendorProduct
mozillathunderbird

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • mozilla thunderbirdbefore 140.7.1
  • mozilla thunderbirdbefore 147.0.1

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

    • 140.7.1 and later · up to and including 140.*not affected · rpm
    • 147.0.1 and laternot affected · rpm

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:11thunderbirdbefore 1:140.7.1esr-1~deb11u11:140.7.1esr-1~deb11u1
Debian:12thunderbirdbefore 1:140.7.1esr-1~deb12u11:140.7.1esr-1~deb12u1
Debian:13thunderbirdbefore 1:140.7.1esr-1~deb13u11:140.7.1esr-1~deb13u1
Debian:14thunderbirdbefore 1:140.7.1esr-11:140.7.1esr-1
openSUSE:Leap 15.6MozillaThunderbirdbefore 140.7.1-150200.8.254.1140.7.1-150200.8.254.1
openSUSE:Leap 16.0MozillaThunderbirdbefore 140.8.1-bp160.1.1140.8.1-bp160.1.1
openSUSE:TumbleweedMozillaThunderbirdbefore 140.7.1-1.1140.7.1-1.1
SUSE:Linux Enterprise Module for Package Hub 15 SP7MozillaThunderbirdbefore 140.7.1-150200.8.254.1140.7.1-150200.8.254.1

Same product

mozilla: all records

Other 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 mess
    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 messages,
    42Plan

Published before and after this one in the same product

  • ← EarlierCVE-2025-5262May 27, 2025 · A double-free could have occurred in `vpx_codec_enc_init_multi` after a failed allocation when initializing the encoder for WebRTC.
    30Monitor
  • ← EarlierCVE-2025-5986Jun 11, 2025 · Unsolicited File Download, Disk Space Exhaustion, and Credential Leakage via mailbox:/// Links
    26Monitor
  • Later →CVE-2026-3889Mar 24, 2026 · Spoofing issue in Thunderbird
    26Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
debian:thunderbird1:140.7.1esr-1~deb12u1 · Debian:12Package registry (OSV)
opensuse:MozillaThunderbird140.7.1-150200.8.254.1 · openSUSE:Leap 15.6Package registry (OSV)
suse:MozillaThunderbird140.7.1-150200.8.254.1 · SUSE:Linux Enterprise Module for Package Hub 15 SP7Package 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.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • A user must open a link or visit a page.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
low · data can be read
Integrity
none
Availability
none
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality impact
Low
Integrity impact
None
Availability impact
None

Weakness class (CWE)

CWE-116 · Improper Encoding or Escaping of Output

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records