CVE-2026-85644: XS::Parse::Infix versions from 0.40 through 0.49 for Perl treat a number as an array reference
XS::Parse::Infix versions from 0.40 through 0.49 for Perl treat a number as an array reference.
The wrapper function XS::Parse::Infix generates for a list-associative infix operator checks whether arguments are array references, but it tests using SvRV() rather than SvROK(). SvRV() reads a union slot that only holds a referent once SvROK(sv) is true, so the guard never validates that it is a reference. For an IV or NV that slot holds the number itself, SvRV() returns the caller's value and SvTYPE() dereferences it at offset 12. This will generally result in a segmentation fault.
An application that hands the wrapper a list built from decoded input (for example, from JSON) lets whoever supplies a number in that list choose the address that the interpreter dereferences.
An ordinary string's byte 12 is rarely SVtPVAV so the guard croaks by luck, but an attacker-crafted string carrying 0x0b there passes, and the buffer is then used as an AV head, with AvARRAY taken from bytes 16-23 and its entries pushed onto the Perl stack as live SVs.
A simple proof-of-concept uses the zip operator:
use Syntax::Operator::Zip 'zip';
my @args = ([1], 2); zip(@args);
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
XS-Parse-Keywordto a version that resolves this vulnerability.Fixed in 0.50
Event History
Frequently Asked Questions
What application pattern makes this reachable from untrusted input?
An application is exposed when it passes a list assembled from decoded attacker-controlled input, such as JSON, to a list-associative infix-operator wrapper generated by XS::Parse::Infix. A supplied number in that list can control the address dereferenced by the Perl interpreter.
Is a numeric value sufficient to trigger a failure?
Yes. The provided proof of concept passes an array reference and the number 2 to the zip operator, which generally causes a segmentation fault. The issue affects the generated argument validation for list-associative infix operators.
Can exploitation go beyond a crash?
Potentially. A crafted string with byte 12 set to 0x0b can pass the faulty type check; its subsequent bytes are treated as an array header, and values from the attacker-controlled buffer can be pushed onto the Perl stack as live SVs.