CVE-2026-87080 Net::IDN::Punycode::PP versions before 2.590 for Perl decode a truncated label to a name containing a character it never encoded in decode_punycode.
A logic error in the pure-Perl Punycode decoder allows inconsistent domain name resolution, potentially enabling security bypasses or phishing.
- 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-2026-87080?
CVE-2026-87080 is a critical 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::PP versions before 2.590 for Perl decode a truncated label to a name containing a character it never encoded in decode_punycode.
The pure-Perl decoder reads one digit at a time with four-argument substr and tests the result with defined to detect the end of the input. substr on an exhausted string returns the empty string rather than undef, so decoding continues past the end. The empty string converts to a digit value below the range, reducing the accumulator, and the decoder derives one extra code point and its position from it. The result is deterministic. The XS backend rejects the same label.
Net::IDN::Punycode uses this backend wherever the XS does not build.
The two backends disagree about what such a label means, so a sender can pick a label that one installation resolves to a name and another rejects.
Weakness: CWE-1286
Which versions are affected by CVE-2026-87080?
How do I fix CVE-2026-87080?
No fix has been published for CVE-2026-87080 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-87080 being exploited?
There is no known exploitation of CVE-2026-87080 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-87080, GHSA-m8c4-89qh-3j3f, UBUNTU-CVE-2026-87080.