Integer signedness error in Glibc before 2.13 and eglibc before 2.13, when using Supplemental Streaming SIMD Extensions 3 (SSSE3) optimization, allows context-dependent attackers to execute arbitrary code via a negative length parameter to (1) memcpy-ssse3-rep.S, (2) memcpy-ssse3.S, or (3) memset-sse2.S in sysdeps/i386/i686/multiarch/, which triggers an out-of-bounds read, as demonstrated using the memcpy function.