# CVE-2026-74766: libnet-idn-encode-perl: Net::IDN::Punycode versions from 2.301 before 2.590 for Perl allow a heap use-after-free via a decoded code point tha...

CVE-2026-74766 is fixed in 4 products on 1 platform, first by DEBIAN-CVE-2026-74766, released September 22, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-74766
- Priority: High
- CVSS: 8.4 (high)
- EPSS: 0.0014
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 22, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libnet-idn-encode-perl Debian 14 | 2.600-1 | [DEBIAN-CVE-2026-74766](https://patchblox.com/security/data/fix/linux/debian-cve-2026-74766.md) | Sep 22, 2026 |
| Linux | perl-Net-IDN-Encode amzn 2023 | 2.590-1.amzn2023.0.1 | [ALAS2023-2026-3190](https://patchblox.com/security/data/fix/linux/alas2023-2026-3190.md) | Nov 7, 2026 |
| Linux | perl-Net-IDN-Encode-debuginfo amzn 2023 | 2.590-1.amzn2023.0.1 | [ALAS2023-2026-3190](https://patchblox.com/security/data/fix/linux/alas2023-2026-3190.md) | Nov 7, 2026 |
| Linux | perl-Net-IDN-Encode-debugsource amzn 2023 | 2.590-1.amzn2023.0.1 | [ALAS2023-2026-3190](https://patchblox.com/security/data/fix/linux/alas2023-2026-3190.md) | Nov 7, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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