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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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
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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-87078 being exploited?
There is no known exploitation of CVE-2026-87078 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-87078, GHSA-xcgq-9mhw-ww57, UBUNTU-CVE-2026-87078.