Add regression test for scanf %mc buffer overflow

This patch adds a regression test for a buffer overflow vulnerability in scanf's %mc format specifier.

By Carlos O'Donell <[email protected]> April 17, 2026 Sentiment 7 / 10

A regression test is being added to stdio-common to verify the fix for bug #34008, which involves a buffer overflow in vfscanf with the %Nmc format specifier. The test is confirmed to fail before the fix and pass after. A copyright correction is requested.

Technical Tradeoffs

Adds a new test case to the test suite.
Requires additional dependencies for the test environment (MALLOC_CHECK_, LD_PRELOAD).

Filed Under: stdioscanfvfscanfregression testsecurity

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