# CVE-2026-116265: MIME::Field::ParamVal versions before 5.521 for Perl do not flag an ambiguous multipart boundary written as RFC 2231 continuations.


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-116265, GHSA-7m3r-rg8x-jrmh, UBUNTU-CVE-2026-116265

## What is CVE-2026-116265?

CVE-2026-116265 is a vulnerability, published on 28 Oct 2026. 

### Official description

MIME::Field::ParamVal versions before 5.521 for Perl do not flag an ambiguous multipart boundary written as RFC 2231 continuations.

The boundary ambiguity checks look only at a plain boundary= parameter, and a boundary split into RFC 2231 sections (boundary*0=, boundary*1= and so on) is joined after they have run. A repeated section number is concatenated rather than reported as a duplicate. From version 5.518, an encoded word or trailing whitespace in such a boundary also goes unflagged, although multipart_boundary() decodes or strips it.

A remote sender can make MIME::Parser split a message on a different boundary than other mail readers, hiding an attachment from a filter that relies on ambiguous_content() while the recipient's mail client shows it.

Weakness: CWE-436 (Interpretation Conflict)

## Which versions are affected by CVE-2026-116265?


## How do I fix CVE-2026-116265?

No fix has been published for CVE-2026-116265 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-116265 being exploited?

There is no known exploitation of CVE-2026-116265 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-116265 and fix it if it is affected.

What it is: CVE-2026-116265 is a vulnerability, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-116265 in the wild and no public exploit code.

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-2026-116265/ (Markdown: https://insights.sbomify.com/CVE-2026-116265/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-116265
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-116265
- OSV: https://osv.dev/vulnerability/CVE-2026-116265

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-116265/
Summaries are generated and may contain mistakes; the official description above is the record.