# CVE-2026-87082: Net::IDN::Punycode versions before 2.590 for Perl hang, crash or return a wrong label via unvalidated malformed UTF-8 in encode_punycode.

> Attackers can cause hangs, crashes, or incorrect label generation in Perl applications by supplying malformed UTF-8 to the Punycode encoder.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 Sep 2026
- **Updated:** 22 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-87082, GHSA-4v8j-337r-265v, UBUNTU-CVE-2026-87082

## What is CVE-2026-87082?

CVE-2026-87082 is a high-severity denial of service vulnerability, published on 22 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Net::IDN::Punycode versions before 2.590 for Perl hang, crash or return a wrong label via unvalidated malformed UTF-8 in encode_punycode.

Neither backend checks that its input is well-formed UTF-8, so a string with the UTF-8 flag set over malformed bytes, as the :utf8 PerlIO layer produces from any malformed input, reaches the encoder unchecked. On perl 5.32 and later the XS backend reports a malformed sequence with a length of `(STRLEN)-1`, so the scan steps back one byte instead of forward and never ends. On earlier perls the XS returns a valid label for a different name. The pure-Perl backend runs a regex over the flagged string. Depending on the bytes, it aborts with SIGBUS on perl 5.28 and later, dies with a panic, or returns a wrong label.

The documented conversion functions match the label against Unicode properties first and that match dies on such a string, so only a direct call to encode_punycode reaches the defect. The decoder is not affected.

A direct caller encoding attacker-supplied bytes hangs, crashes or gets a label for a name the input never held.

Weakness: CWE-835 (Loop with Unreachable Exit Condition), CWE-1286 (Improper Validation of Syntactic Correctness of Input)

## Which versions are affected by CVE-2026-87082?


## How do I fix CVE-2026-87082?

No fix has been published for CVE-2026-87082 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-87082 being exploited?

There is no known exploitation of CVE-2026-87082 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-87082 and fix it if it is affected.

What it is: CVE-2026-87082 is a high-severity denial of service vulnerability, published on 22 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-87082 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-2026-87082/ (Markdown: https://insights.sbomify.com/CVE-2026-87082/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-87082
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-87082
- OSV: https://osv.dev/vulnerability/CVE-2026-87082

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-87082/
Summaries are generated and may contain mistakes; the official description above is the record.