# CVE-2026-87080: Net::IDN::Punycode::PP versions before 2.590 for Perl decode a truncated label to a name containing a character it never encoded in decode_punycode.

> A logic error in the pure-Perl Punycode decoder allows inconsistent domain name resolution, potentially enabling security bypasses or phishing.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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-2026-87080, GHSA-m8c4-89qh-3j3f, UBUNTU-CVE-2026-87080

## What is CVE-2026-87080?

CVE-2026-87080 is a critical 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::PP versions before 2.590 for Perl decode a truncated label to a name containing a character it never encoded in decode_punycode.

The pure-Perl decoder reads one digit at a time with four-argument substr and tests the result with defined to detect the end of the input. substr on an exhausted string returns the empty string rather than undef, so decoding continues past the end. The empty string converts to a digit value below the range, reducing the accumulator, and the decoder derives one extra code point and its position from it. The result is deterministic. The XS backend rejects the same label.

Net::IDN::Punycode uses this backend wherever the XS does not build.

The two backends disagree about what such a label means, so a sender can pick a label that one installation resolves to a name and another rejects.

Weakness: CWE-1286 (Improper Validation of Syntactic Correctness of Input)

## Which versions are affected by CVE-2026-87080?


## How do I fix CVE-2026-87080?

No fix has been published for CVE-2026-87080 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-87080 being exploited?

There is no known exploitation of CVE-2026-87080 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-87080 and fix it if it is affected.

What it is: CVE-2026-87080 is a critical 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-2026-87080 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-2026-87080/ (Markdown: https://insights.sbomify.com/CVE-2026-87080/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-87080
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-87080
- OSV: https://osv.dev/vulnerability/CVE-2026-87080

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-87080/
Summaries are generated and may contain mistakes; the official description above is the record.