Nodemailer addressparser: O(n^2) on comment-joined addresses enables a remote DoS (reachable via mailparser)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-90776: 0.68% estimated exploitation activity in the next 30 days; percentile 52.62 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary nodemailer/lib/addressparser parses one shape of address in O(n^2) time. A single ~640 KB address value blocks the Node.js event loop for roughly 7 seconds. And it is reachable without auth: mailparser feeds inbound email headers straight into this parser, so one crafted email is enough to stall a service that parses mail. Details The parser builds a single address by accumulating its atoms into one string. When the atoms are separated by RFC 5322 comments, like a@b(c)@b(c)@b(c)..., every atom re-joins that same growing string. The join check in src/addressparser/index.ts: The issue is the order of the last two operands. parts[parts.length - 1].slice(-1) runs before the cheap token.value.charAt(0). slice(-1) has to flatten the accumulator to read its last character → O(current length) → and that runs on every token → O(n^2) over the whole value. Since || is left to right, the cheap charAt(0) that would short-circuit never gets the chance. The chain: long comment-joined…

Published by the source

30 Sep 2026, 14:41 UTC

Last modified by the source

5 Oct 2026, 23:45 UTC

Source last checked

26 Oct 2026, 13:06 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-prgh-xp8r-p3m5

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-prgh-xp8r-p3m5

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-prgh-xp8r-p3m5

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# Patch Next advisory brief: CVE-2026-90776

Advisory: Nodemailer addressparser: O(n^2) on comment-joined addresses enables a remote DoS (reachable via mailparser)
IDs: CVE-2026-90776, GHSA-prgh-xp8r-p3m5
Record: https://patchnext.com/advisories/cve-2026-90776 (revision 3, source checked 26 Oct 2026, 13:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nodemailer 10.0.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm nodemailer: affected >= 9.1.0, <= 10.0.4; fixed in 10.0.5

## Suggested inspection (read-only)
- `npm ls nodemailer --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nodemailer.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-prgh-xp8r-p3m5 (GitHub-reviewed advisory GHSA-prgh-xp8r-p3m5 lists affected ranges: npm nodemailer >=9.1.0 <=10.0.4)
- Verified: https://osv.dev/vulnerability/GHSA-prgh-xp8r-p3m5 (OSV record GHSA-prgh-xp8r-p3m5 lists affected ranges: npm nodemailer >=9.1.0 <10.0.5 (fixed))

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