zbateson mail-mime-parser before 3.0.9 and 4.x before 4.0.6 CRLF Header Injection via Message Builders
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- Proof of concept public, per CISA
- Fix
- Fixed in 3.0.9, 4.0.6
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 3.0.9, 4.0.6.
- Exploitation15/40CISA rates a proof of concept as public
- Exposure20/25No login or user action needed per the CVSS vector, CISA rates it automatable · Data gap: No advisory context yet
- Reach?/20Reach: unknown (data gap). No tracked technology or package matched
- Severity6.9/10CVSS 6.9
- No patch0/5No signal
What would change the score
- Would score about 72 if added to CISA KEV
- Would score about 67 if CISA's SSVC rates exploitation active
- Would score about 47 if advisories confirm default setups are exposed
CVE-2026-121946 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.9 (medium) and affects mail-mime-parser; fixed in 3.0.9 and 4.0.6.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 42/100 · provisional
- Fix
- Fixed in 3.0.9, 4.0.6
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: poc
- Automatable: yes
- Technical impact: partial
Summary
The zbateson mail-mime-parser library, used to build MIME email messages, is affected by a CRLF header injection flaw in its message-building helpers. A remote attacker who can supply crafted MIME type, charset, encoding, micalg, or protocol values, without logging in or any user action, can inject extra header lines such as a forged Bcc into outgoing messages.
Read the original description
zbateson mail-mime-parser before 3.0.9 and 4.x before 4.0.6 contains a CRLF header injection vulnerability in message-building helpers that fail to strip CR and LF characters. Attackers supplying crafted MIME type, charset, encoding, micalg, or protocol values can inject extra header lines such as a forged Bcc into outgoing messages.
What to do
Upgrade to a fixed version: 3.0.9, 4.0.6.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: poc · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- zbateson mail-mime-parser
From 0.3.0 · fixed in 3.0.9; From 4.0.0 · fixed in 4.0.6
Evidence 7
- Advisory
- Patch
- Patch
- Patch
- Patch
Corrections
None so far.
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Questions about CVE-2026-121946
Is CVE-2026-121946 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-121946?
mail-mime-parser: from 0.3.0 before 3.0.9; from 4.0.0 before 4.0.6.Source: cve.now feed data
How do I fix CVE-2026-121946?
Upgrade to a fixed version: 3.0.9, 4.0.6.Source: cve.now feed data