An out of bounds write was possible within ClamAV's NSIS bzip2 library when attempting decompression in cases where the number of selectors exceeded the max limit set by the library (CVE-2019-12900).
The decompressor used in bzip2 contains a bug which can lead to an out-of-bounds write when processing a specially crafted bzip2(1) file. bzip2recover contains a heap use-after-free bug which can be triggered when processing a specially crafted bzip2(1) file. An attacker who can cause maliciously crafted input to be processed may trigger either of these bugs. The bzip2recover bug may cause a crash, permitting a denial-of-service. The bzip2 decompressor bug could potentially be exploited to execute arbitrary code. Note that some utilities, including the tar(1) archiver and the bspatch(1) binary patching utility (used in portsnap(8) and freebsd-update(8)) decompress bzip2(1)-compressed data internally; system administrators should assume that their systems will at some point decompress bzip2(1)-compressed data even if they never explicitly invoke the bunzip2(1) utility.