Use-after-free vulnerability in the phar_rename_archive function in phar_object.c in PHP before 5.5.22 and 5.6.x before 5.6.6 allows remote attackers to cause a denial of service or possibly have unspecified other impact via vectors that trigger an attempted renaming of a Phar archive to the name of an existing file.
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.