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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
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
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.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-74766 being exploited?
There is no known exploitation of CVE-2026-74766 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-74766, GHSA-qffm-j59f-77qw, UBUNTU-CVE-2026-74766.