stack_protect_prologue in cfgexpand.c and stack_protect_epilogue in function.c in GNU Compiler Collection (GCC) 4.1 through 8 (under certain circumstances) generate instruction sequences when targeting ARM targets that spill the address of the stack protector guard, which allows an attacker to bypass the protection of -fstack-protector, -fstack-protector-all, -fstack-protector-strong, and -fstack-protector-explicit against stack overflow by controlling what the stack canary is compared against.

References

• https://nvd.nist.gov/vuln/detail/CVE-2018-12886
• https://gcc.gnu.org/viewcvs/gcc/trunk/gcc/config/arm/arm-protos.h?revision=266379&view=markup
• https://www.gnu.org/software/gcc/gcc-8/changes.html