CVE-2018-25032

An out-of-bounds access flaw was found in zlib, which allows memory corruption when deflating (ex: when compressing) if the input has many distant matches. For some rare inputs with a large number of distant matches (crafted payloads), the buffer into which the compressed or deflated data is written can overwrite the distance symbol table which it overlays. This issue results in corrupted output due to invalid distances, which leads to out-of-bound access, corrupting the memory and potentially crashing the application.

This bug was introduced in zlib v1.2.2.2 through zlib v1.2.11, with the addition of the Z_FIXED option, which forces the use of fixed Huffman codes, rather than dynamic Huffman codes, allowing for a simpler decoder for special applications.

This bug is difficult to trigger, as Z_FIXED is usually only used in special circumstances.

Rsync does the compression in-transit using zlib. As rsync uses vulnerable zlib v1.2.8 package, which incorrectly handles memory when performing certain zlib compressing or deflating operations. This results in rsync to crash.

Note - The issue wasn't publicly labelled as security vulnerability until 2022, but the fix was public since 2018.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.