AIKIDO-2026-11069
psych is vulnerable to Heap-based Buffer Overflow
31
Low Risk
This Affects:
psychTL;DR
The io_reader callback in the libyaml C extension copies RSTRING_LEN bytes from the value returned by the wrapping Ruby IO#read into libyaml's fixed-capacity buffer without validating the returned length against the requested size. When a non-standard IO-like object's #read over-returns, the memcpy writes past the end of libyaml's buffer, causing a heap out-of-bounds write reachable through Psych.load, Psych.safe_load, and Psych.parse. The fix clamps the copy length to the requested buffer size before the memcpy.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range.
Background info
psych is vulnerable to Heap-based Buffer Overflow in versions 2.0.0 - 5.3.1.
How to fix this
Upgrade the psych library to the patch version.
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