CVE-2020-12397Network attack vector

Sender spoofing via unnormalized encoded Unicode whitespace

Published May 22, 2020 · Updated Aug 4, 2024

Origin validation error in Mozilla Thunderbird before 68.8.0 allows remote attackers to spoof the displayed sender address in crafted email. The Message Reader UI decodes RFC 2047 From-header tokens without applying cleanToken to encoded Unicode whitespace, so invisible spacing conceals the real address. The recipient must display the crafted message and trust its shown From identity; the bounded consequence is message-origin misrepresentation.

CVSS severity4.3
Medium
EPSS probability0.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Origin validation error in Mozilla Thunderbird before 68.8.0 allows remote attackers to spoof the displayed sender address in crafted email. The Message Reader UI decodes RFC 2047 From-header tokens without applying cleanToken to encoded Unicode whitespace, so invisible spacing conceals the real address. The recipient must display the crafted message and trust its shown From identity; the bounded consequence is message-origin misrepresentation.

The record

CVE
CVE-2020-12397
Published
May 22, 2020
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Thunderbird
Classifications
CWE-346, T1036
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 22, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <68.8.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Thunderbirdversion=unspecified <68.8.0

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-346Origin Validation Error
T1036Masquerading

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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