The disas_insn function in target/i386/translate.c in QEMU before 2.9.0, when TCG mode without hardware acceleration is used, does not limit the instruction size, which allows local users to gain privileges by creating a modified basic block that injects code into a setuid program, as demonstrated by procmail. NOTE: the vendor has stated "this bug does not violate any security guarantees QEMU makes.
https://github.com/qemu/qemu/commit/30663fd26c0307e414622c7a8607fbc04f92ec14
https://bugs.chromium.org/p/project-zero/issues/detail?id=1122