Out-of-Bounds Read in Perl Net::IDN::Punycode XS Backend
CVE-2026-74765 is an integer overflow leading to an out-of-bounds read vulnerability in the XS backend of the Net::IDN::Punycode Perl module. The flaw is triggered when encoding a sufficiently long or specially crafted Punycode label, causing the delta accumulator to overflow and bypass an array bounds check, allowing a read from outside the intended digit table. A successful attack could crash the affected process or potentially leak memory contents. The vulnerability is currently assigned a CVSS v3.1 base score of 6.5 (Medium). No public proof-of-concept or known in-the-wild exploitation has been reported.
What to do: Update the Net::IDN::Punycode Perl module to version 2.590 or later, which contains the fix for this vulnerability. Review any Perl applications using this library to ensure they are patched.
| Product | Affected |
|---|---|
| Net::IDN::Punycode | before 2.590 |
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
Net::IDN::Punycode versions before 2.590 for Perl allow an out-of-bounds read via integer overflow of the delta accumulator in encode_punycode. The XS backend keeps the punycode delta, and the digit index derived from it, in a signed int. The accumulation `delta += (m-n) * (h+1)` has no overflow check, so a large enough code point wraps the delta and the digit index leaves the range of the 36-entry digit table. The bound before the final table access tests only for an index above 36, so a negative index passes it, as does 36 itself. Perl strings hold code points beyond the Unicode range, and one such code point overflows the accumulation on its own. Valid input wraps it as well, for example 1927 ASCII letters followed by U+10FFFF. The conversion functions encode a label before they check its length, so a long label reaches the encoder through the documented API. Only the XS backend is affected. Encoding an attacker-supplied string copies a byte from outside the digit table into the encoded result or crashes the process.
Perl Net::IDN::Punycode before 2.590 allows an out-of-bounds read via delta overflow in encode_punycode.
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