CVE-2021-33833: 
Linux Debian vulnerability analysis and mitigation

ConnMan (Connection Manager) versions 1.30 through 1.39 contained a stack-based buffer overflow vulnerability in the uncompress function within dnsproxy.c. The vulnerability, identified as CVE-2021-33833, was discovered by Mike Evdokimov at Digital Security and disclosed on June 9, 2021. The vulnerability affects the DNS proxy component and can be triggered via NAME, RDATA, or RDLENGTH fields for A or AAAA record types (OSS Security).

The vulnerability exists in the uncompress function of dnsproxy.c where insufficient bounds checking during memcpy operations could lead to a stack buffer overflow. The issue specifically involves the processing of NAME and RDATA/RDLENGTH fields with TYPE A/AAAA DNS records. The vulnerability can be exploited when processing DNS server replies, allowing malicious remote DNS servers to trigger the overflow condition (OSS Security).

While the vulnerability could potentially lead to arbitrary code execution, the presence of stack overflow protection mechanisms appears to mitigate the severity of the exploit. A proof-of-concept exploit was developed but only worked with stack overflow heuristics and PIE (Position Independent Executable) disabled, suggesting that standard security protections effectively limit the impact (OSS Security).

The issue was fixed in ConnMan version 1.40. A patch was developed by r.alyautdin@digitalrussia.ru and implemented by the upstream ConnMan team. The fix involves adding proper length checks before memcpy operations in the affected code. Users are advised to upgrade to ConnMan version 1.40 or later to address this vulnerability (Gentoo Security, OSS Security).