XZ Utils provide a general-purpose data-compression library plus command-line tools. Prior to version 5.8.3, if lzma_index_decoder() was used to decode an Index that contained no Records, the resulting lzma_index was left in a state where where a subsequent lzma_index_append() would allocate too little memory, and a buffer overflow would occur. This issue has been patched in version 5.8.3.

Malicious code was discovered in the upstream tarballs of xz, starting with version 5.6.0. Through a series of complex obfuscations, the liblzma build process extracts a prebuilt object file from a disguised test file existing in the source code, which is then used to modify specific functions in the liblzma code. This results in a modified liblzma library that can be used by any software linked against this library, intercepting and modifying the data interaction with this library.

An issue discovered in XZ 5.2.5 allows attackers to cause a denial of service via decompression of a crafted file. NOTE: the vendor disputes the claims of "endless output" and "denial of service" because decompression of the 17,486 bytes always results in 114,881,179 bytes, which is often a reasonable size increase.

An arbitrary file write vulnerability was found in GNU gzip's zgrep utility. When zgrep is applied on the attacker's chosen file name (for example, a crafted file name), this can overwrite an attacker's content to an arbitrary attacker-selected file. This flaw occurs due to insufficient validation when processing filenames with two or more newlines where selected content and the target file names are embedded in crafted multi-line file names. This flaw allows a remote, low privileged attacker to force zgrep to write arbitrary files on the system.

scripts/xzgrep.in in xzgrep 5.2.x before 5.2.0, before 5.0.0 does not properly process file names containing semicolons, which allows remote attackers to execute arbitrary code by having a user run xzgrep on a crafted file name.