# CVE-2026-26312: Stalwart Mail Server has Out-of-Memory Denial of Service via Malformed Nested MIME Messages

> Attackers can crash Stalwart Mail Server by sending malformed nested MIME emails, causing excessive resource consumption and out-of-memory conditions.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 19 Feb 2026
- **Updated:** 20 Feb 2026
- **Also known as:** GHSA-jm95-876q-c9gw

## What is CVE-2026-26312?

CVE-2026-26312 is a medium-severity denial of service vulnerability in stalwartlabs stalwart, published on 19 Feb 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Stalwart is a mail and collaboration server. A denial-of-service vulnerability exists in Stalwart Mail Server versions 0.13.0 through 0.15.4 where accessing a specially crafted email containing malformed nested `message/rfc822` MIME parts via IMAP or JMAP causes excessive CPU and memory consumption, potentially leading to an out-of-memory condition and server crash. The malformed structure causes the `mail-parser` crate to produce cyclical references in its parsed representation, which Stalwart then follows indefinitely. Version 0.15.5 contains a patch.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-26312?

It affects 1 product.


Products: Stalw Stalwart.

## How do I fix CVE-2026-26312?

No fix has been published for CVE-2026-26312 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-26312 being exploited?

There is no known exploitation of CVE-2026-26312 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-26312 and fix it if it is affected.

What it is: CVE-2026-26312 is a medium-severity denial of service vulnerability in stalwartlabs stalwart, published on 19 Feb 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-26312 in the wild and no public exploit code.

Affected product: stalwartlabs stalwart. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-26312/ (Markdown: https://insights.sbomify.com/CVE-2026-26312/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-26312
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-26312
- OSV: https://osv.dev/vulnerability/CVE-2026-26312

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-26312/
Summaries are generated and may contain mistakes; the official description above is the record.