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

CVE-2026-87078 is fixed in 4 products on 1 platform, first by DEBIAN-CVE-2026-87078, released September 22, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2026-87078
- Priority: Urgent
- CVSS: 9.1 (critical)
- EPSS: 0.0039
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 22, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | libnet-idn-encode-perl Debian 14 | 2.600-1 | [DEBIAN-CVE-2026-87078](https://patchblox.com/security/data/fix/linux/debian-cve-2026-87078.md) | Sep 22, 2026 |
| Linux | perl-Net-IDN-Encode Fedora 43 | 2.502-1.fc43 | [FEDORA-2026-4AEC7019EB](https://patchblox.com/security/data/fix/linux/fedora-2026-4aec7019eb.md) | Nov 7, 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 Fedora 43 | 2.502-1.fc43 | [FEDORA-2026-4AEC7019EB](https://patchblox.com/security/data/fix/linux/fedora-2026-4aec7019eb.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 Fedora 43 | 2.502-1.fc43 | [FEDORA-2026-4AEC7019EB](https://patchblox.com/security/data/fix/linux/fedora-2026-4aec7019eb.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 2026-11-09T19:38:12Z 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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