Off-by-one error in the encodes function in pack.c in Ruby 1.9.3 and earlier, and 2.x through 2.1.2, when using certain format string specifiers, allows context-dependent attackers to cause a denial of service (segmentation fault) via vectors that trigger a stack-based buffer overflow.
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.