# CVE-2026-100889: Trusted Domain Project OpenDKIM Decoder util.c dkim_qp_decode off-by-one

> Remote attackers can exploit an off-by-one error in OpenDKIM's decoder to potentially execute code or cause denial of service.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 27 Sep 2026
- **Updated:** 28 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-100889, GHSA-87hw-mmxf-r6m3, UBUNTU-CVE-2026-100889

## What is CVE-2026-100889?

CVE-2026-100889 is a medium-severity vulnerability in Trusted Domain Project OpenDKIM, published on 27 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability was detected in Trusted Domain Project OpenDKIM up to 2.11.0. Affected is the function dkim_qp_decode of the file util.c of the component Decoder. The manipulation results in off-by-one. The attack may be performed from remote. The exploit is now public and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

Weakness: CWE-193 (Off-by-one Error), CWE-189

## Which versions are affected by CVE-2026-100889?


## How do I fix CVE-2026-100889?

No fix has been published for CVE-2026-100889 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100889 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100889 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100889 and fix it if it is affected.

What it is: CVE-2026-100889 is a medium-severity vulnerability in Trusted Domain Project OpenDKIM, published on 27 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100889 exists.

Affected product: Trusted Domain Project OpenDKIM. 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-2026-100889/ (Markdown: https://insights.sbomify.com/CVE-2026-100889/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100889
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100889
- OSV: https://osv.dev/vulnerability/CVE-2026-100889

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-100889/
Summaries are generated and may contain mistakes; the official description above is the record.