# CVE-2026-74766: Net::IDN::Punycode versions from 2.301 before 2.590 for Perl allow a heap use-after-free via a decoded code point that reallocates the outpu

> A heap use-after-free in the Perl Net::IDN::Punycode library allows attackers to execute code or cause denial of service via crafted punycode labels.

- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 Sep 2026
- **Updated:** 22 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-74766, GHSA-qffm-j59f-77qw, UBUNTU-CVE-2026-74766

## What is CVE-2026-74766?

CVE-2026-74766 is a high-severity use after free vulnerability, published on 22 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Net::IDN::Punycode versions from 2.301 before 2.590 for Perl allow a heap use-after-free via a decoded code point that reallocates the output buffer in decode_punycode.

The XS backend inserts each decoded code point into the string buffer of the scalar it returns. decode_punycode computes the insertion pointer first and only then grows the buffer when the code point does not fit. The growth reallocates the buffer and updates every pointer except the insertion pointer, so the move that follows and the write of the code point go through a freed pointer. The buffer starts at twice the label length, and a code point above U+FFFF takes four bytes in the output, so a label of such code points outgrows it and forces the reallocation.

Version 2.301, the fix for CVE-2016-15059, introduced the defect. Only the XS backend is affected.

Decoding an attacker-supplied punycode label reads and writes freed heap memory.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-74766?


## How do I fix CVE-2026-74766?

No fix has been published for CVE-2026-74766 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-74766 being exploited?

There is no known exploitation of CVE-2026-74766 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74766 and fix it if it is affected.

What it is: CVE-2026-74766 is a high-severity use after free vulnerability, published on 22 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74766 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-2026-74766/ (Markdown: https://insights.sbomify.com/CVE-2026-74766/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74766
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74766
- OSV: https://osv.dev/vulnerability/CVE-2026-74766

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74766/
Summaries are generated and may contain mistakes; the official description above is the record.