# CVE-2026-100888: Trusted Domain Project OpenDKIM DKIM Signature Header Selection dkim-canon.c dkim_canon_selecthdrs out-of-bounds write

> Remote attackers can trigger an out-of-bounds write in OpenDKIM via crafted DKIM headers, potentially leading to code execution or service crashes.

- **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:** 30 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-100888, GHSA-wm7g-7hm5-7hfr, UBUNTU-CVE-2026-100888

## What is CVE-2026-100888?

CVE-2026-100888 is a medium-severity memory corruption 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 weakness has been identified in Trusted Domain Project OpenDKIM up to 2.11.0. This affects the function dkim_canon_selecthdrs of the file libopendkim/dkim-canon.c of the component DKIM Signature Header Selection. Executing a manipulation of the argument h can lead to out-of-bounds write. The attack can be executed remotely. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.

Weakness: CWE-787 (Out-of-bounds Write), CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2026-100888?


## How do I fix CVE-2026-100888?

No fix has been published for CVE-2026-100888 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100888 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100888 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100888 and fix it if it is affected.

What it is: CVE-2026-100888 is a medium-severity memory corruption 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-2026-100888 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-2026-100888/ (Markdown: https://insights.sbomify.com/CVE-2026-100888/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100888
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100888
- OSV: https://osv.dev/vulnerability/CVE-2026-100888

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-100888/
Summaries are generated and may contain mistakes; the official description above is the record.