CVE-2018-25032: Zlib Deflate Memory Corruption Vulnerability

CVE-2018-25032 identifies a memory corruption vulnerability in zlib library versions before 1.2.12 that enables denial of service attacks through crafted compression input containing many distant matches. This vulnerability affects zlib versions 1.2.2.2 through 1.2.11, achieving a CVSS score of 7.5 (High severity) with an EPSS score of 26 percentile and 0.1% exploitation probability, indicating moderate risk primarily focused on availability impact. The vulnerability details reveal that the deflate compression algorithm contains a buffer management flaw where the pending buffer can overwrite the distance symbol table during compression of specially crafted input, leading to memory corruption and potential application crashes. This creates substantial exploit risk for applications and systems that process untrusted compressed data using zlib, particularly affecting MySQL, MariaDB Server, and over 31 other technologies that rely on zlib for compression functionality, including web servers, databases, file compression utilities, and network applications that handle user-supplied compressed content through Nokogiri and similar libraries. The technical root cause lies in zlib's deflateInit2_() and deflateCopy() functions, which establish a flawed memory layout where the pending_buf overlays with symbol tables (d_buf and l_buf), classified as CWE-787 (Out-of-bounds Write), creating a vector for known exploited vulnerabilities targeting compression libraries. The vulnerability specifically affects the compress_block() function's interaction with corrupted symbol tables, where improper buffer management during Z_FIXED option processing allows the pending buffer to overwrite distance and literal/length symbol tables, resulting in invalid compression output and potential out-of-bounds memory access. Originally discovered by Danilo Ramos in 2018 but not patched until zlib 1.2.12, this vulnerability was rediscovered by Tavis Ormandy in 2022, prompting widespread security advisories from major vendors including Apple, Debian, Fedora, and NetApp. Mitigation strategies require upgrading to zlib version 1.2.12 or later, which implements a combined symbol buffer approach that prevents pending buffer overwrites by ensuring proper spacing between compression buffers and symbol tables. Organizations should prioritize identifying all applications and systems using vulnerable zlib versions, implement input validation for compression operations to detect potentially malicious patterns, monitor compression processes for unusual memory usage or crashes, and maintain updated CVE database records to track similar memory corruption vulnerabilities that could compromise application stability through unsafe buffer management and compression algorithm exploitation in data processing systems.