VulnerabilityPublished 4 Nov 2026

CVE-2026-121946: zbateson mail-mime-parser · CRLF Injection

Affects zbateson mail-mime-parserSource CVE Database V5

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Not known to be exploited · CVSS 6.9 Medium : upgrade to 4.0.6 or 3.0.9 when convenient.

Data as of 4 Nov 2026, 12:59 UTC

CVSS 4.0 base score

6.9Medium

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (VulnCheck)	CVSS 4.0	6.9
CNA (VulnCheck)	CVSS 3.1	7.2

Patch: Available – fixed in 4.0.6, 3.0.9

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: Low
Vulnerable system integrity: Low
Vulnerable system availability: None
Subsequent system confidentiality: Low
Subsequent system integrity: Low
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the Vulnerable System.
Vulnerable system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the Subsequent System.
Subsequent system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Subsequent System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 4 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade zbateson mail-mime-parser to 4.0.6 or 3.0.9.

Affected software

Product	Affected	Fixed in
zbatesonmail-mime-parser	Affected >=4.0.0 <4.0.6	Fixed in 4.0.6
zbatesonmail-mime-parser	Affected >=0.3.0 <3.0.9	Fixed in 3.0.9
Packagistmail-mime-parser`pkg:composer/mail-mime-parser`Other threats	Affected >=0.3.0 <3.0.9 >=4.0.0 <4.0.6	Fixed in 3.0.9 4.0.6

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade zbateson mail-mime-parser to version 3.0.9 or later, or 4.0.6 or later, where this CRLF injection vulnerability is fixed. No other mitigation is indicated by the vendor advisory.

Description

zbateson mail-mime-parser versions before 3.0.9 and 4.x before 4.0.6 have a CRLF injection vulnerability. This flaw occurs in message-building helpers that do not properly strip carriage return (CR) and line feed (LF) characters from certain header fields. An attacker can exploit this by supplying crafted MIME type, charset, encoding, micalg, or protocol values to inject additional header lines, such as a forged Bcc, into outgoing email messages.

Impact

The vulnerability allows attackers to inject arbitrary additional email header lines into outgoing messages. This can lead to unauthorized modification of email headers, such as forging Bcc recipients. While the CVSS score is 6.9 (medium severity), the impact is limited to header manipulation without direct privilege escalation or remote code execution. There are no known exploits in the wild at this time.

Summary

CVE-2026-121946 is a CRLF header injection vulnerability in zbateson mail-mime-parser affecting versions >=0.3.0 <3.0.9 and >=4.0.0 <4.0.6. The vulnerability arises because message-building helper functions fail to sanitize CR and LF characters in MIME header fields. This allows attackers to inject extra header lines into email messages, potentially manipulating email headers such as adding forged Bcc recipients. The issue is fixed in versions 3.0.9 and 4.0.6.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 4 Nov 2026, 12:45 UTC

Technical details

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