# CVE-2026-87079: Net::IDN::Punycode versions before 2.590 for Perl allow CPU exhaustion via quadratic insertion cost when decoding a long label in decode_punycode.

> Attackers can cause CPU exhaustion in Perl applications using Net::IDN::Punycode by supplying long labels, leading to denial of service.

- **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-2026-87079, GHSA-vx57-287r-4h84, UBUNTU-CVE-2026-87079

## What is CVE-2026-87079?

CVE-2026-87079 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 allow CPU exhaustion via quadratic insertion cost when decoding a long label in decode_punycode.

The XS backend inserts each decoded code point into a UTF-8 buffer and finds the insertion point by scanning that buffer from the start, one character at a time. The scan runs once per code point over the output built so far, so the cost is quadratic in the label length. The pure-Perl backend downgrades its input to bytes so that substr can index it directly, but takes its working copy before the downgrade, so when the input carries the UTF-8 flag every substr on the copy scans from the start, with the same quadratic cost.

Nothing bounds the label length in the to-Unicode direction. The 63-byte DNS limit is checked only when converting to ASCII, so domain_to_unicode and uts46_to_unicode pass an attacker-supplied label of any length to the decoder.

Weakness: CWE-407 (Inefficient Algorithmic Complexity)

## Which versions are affected by CVE-2026-87079?


## How do I fix CVE-2026-87079?

No fix has been published for CVE-2026-87079 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-87079 being exploited?

There is no known exploitation of CVE-2026-87079 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-87079 and fix it if it is affected.

What it is: CVE-2026-87079 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-2026-87079 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-2026-87079/ (Markdown: https://insights.sbomify.com/CVE-2026-87079/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-87079
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-87079
- OSV: https://osv.dev/vulnerability/CVE-2026-87079

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-87079/
Summaries are generated and may contain mistakes; the official description above is the record.