CVE-2021-23400Public exploitNetwork attack vector

Arbitrary mail header injection via address objects

Published Jun 29, 2021 · Updated Sep 16, 2024

HTTP header injection in Nodemailer before 6.6.1 allows remote attackers to add arbitrary mail headers through a crafted address object. MimeNode._normalizeAddress() trims the address string but leaves carriage returns and line feeds intact before _convertAddresses() inserts it into a generated header. Exploitation requires an application to pass attacker-controlled address-object input into message construction; the resulting email can carry attacker-chosen headers.

CVSS severity6.3
Medium
EPSS probability1.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP header injection in Nodemailer before 6.6.1 allows remote attackers to add arbitrary mail headers through a crafted address object. MimeNode._normalizeAddress() trims the address string but leaves carriage returns and line feeds intact before _convertAddresses() inserts it into a generated header. Exploitation requires an application to pass attacker-controlled address-object input into message construction; the resulting email can carry attacker-chosen headers.

The record

CVE
CVE-2021-23400
Published
Jun 29, 2021
Updated
Sep 16, 2024
Vendor
Nodemailer
Product
Nodemailer
Classifications
CWE-74
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 29, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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 <6.6.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Nodemailer · Nodemailerversion=unspecified <6.6.1

Published CVSS scores

8.8NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:P/I:P/A:P
6.3GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L

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.

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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 exploitPublished

Weakness, pattern, technique

CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

Public exploit references

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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