# CVE-2026-87078: Net::IDN::Punycode versions from 2.302 before 2.590 for Perl leak the output buffer on every rejected label in decode_punycode.

> Attackers can cause memory exhaustion and denial of service by sending invalid Punycode labels to the Perl Net::IDN::Punycode library.

- **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-2026-87078, GHSA-xcgq-9mhw-ww57, UBUNTU-CVE-2026-87078

## What is CVE-2026-87078?

CVE-2026-87078 is a critical 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 from 2.302 before 2.590 for Perl leak the output buffer on every rejected label in decode_punycode.

The XS backend allocates the scalar it returns before it validates the input, sizing the buffer at twice the input length. The scalar is released only on the success path, so each of the three croaks that reject a label leaves the scalar and its buffer allocated. Nothing bounds the label length in the to-Unicode direction, since the 63-byte DNS limit is checked only when converting to ASCII.

Only the XS backend is affected.

A sender who supplies invalid labels grows the process by twice the label length per rejected call, with no successful call needed.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2026-87078?


## How do I fix CVE-2026-87078?

No fix has been published for CVE-2026-87078 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-87078 being exploited?

There is no known exploitation of CVE-2026-87078 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-87078 and fix it if it is affected.

What it is: CVE-2026-87078 is a critical 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-2026-87078 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-2026-87078/ (Markdown: https://insights.sbomify.com/CVE-2026-87078/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-87078
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-87078
- OSV: https://osv.dev/vulnerability/CVE-2026-87078

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-87078/
Summaries are generated and may contain mistakes; the official description above is the record.