CVE-2026-29518

rsync versions 3.1.0 through before 3.5.0 contain a signed integer overflow vulnerability in the I/O timeout implementation. Attackers can inject MSG_IO_TIMEOUT messages with non-positive values, causing the timeout variable to wrap and permanently disabling connection timeouts, allowing idle connections to hold daemon slots indefinitely and leading to resource exhaustion.

rsync versions 3.0.0 before 3.5.0 contain an out-of-bounds write vulnerability that allows attackers to corrupt memory by triggering HLINK_BUMP processing on file entries with the FLAG_HLINKED flag set while the hard-link preservation option is inactive. Attackers can exploit the missing F_SUM field in the file_struct layout to access memory past the end of the allocated structure, corrupting adjacent heap or stack data.

rsync versions 3.2.0 through 3.2.3 (openssl mode) and rsync-ssl through 3.4.4 (stunnel mode) contain a TLS certificate validation vulnerability that allows on-path attackers to intercept encrypted sessions by presenting self-signed or otherwise invalid certificates. Attackers can exploit the failure to validate server TLS certificates against a trusted CA or verify certificate hostname matching to decrypt or tamper with rsync session content without detection by the client.

rsync before 3.5.0 contains a logic error in --max-alloc handling that allows a sender or configuration setting --max-alloc=0 to disable allocation sanity checks entirely rather than enforcing a zero-byte cap. Attackers can exploit this flaw to cause the receiver to attempt unbounded memory allocations for file list and data structures, potentially exhausting available memory and causing a denial of service.

rsync before 3.5.0 contains multiple command and argument injection vulnerabilities that allow attackers to execute arbitrary commands by supplying malicious input through several code paths, including the RSYNC_CONNECT_PROG environment variable, daemon hooks, the rsync-ssl wrapper, and remote-shell command newline injection. Attackers can inject shell metacharacters or newline characters into unsanitized user-supplied values such as hostnames and hostspecs to execute arbitrary commands under the privileges of the rsync process or the invoking user.

rsync before 3.5.0 contains a path traversal vulnerability that allows a malicious sender to write files outside the intended destination directory tree by crafting relative paths with symlink components in --relative mode. The make_path() function follows symlinks pointing outside the destination tree while creating intermediate directories without verifying that created paths remain within the destination boundary, enabling arbitrary file writes on the receiver's filesystem.

The check_secret function in rsync 3.1.0 and earlier allows remote attackers to cause a denial of service via a user name which does not exist in the secrets file, leading to an infinite loop and CPU consumption.

The rsync daemon before version 3.5.0 contains an IP address spoofing vulnerability that allows unauthenticated remote attackers to bypass IP-based access controls by sending a crafted PROXY protocol header with a forged source address. Attackers who can connect directly to the rsync daemon can inject a spoofed source IP in the PROXY protocol header to circumvent hosts allow/deny rules, gaining unauthorized access that would otherwise be blocked based on their real source address.

A heap-based buffer overflow vulnerability was found in the rsync daemon due to improper handling of attacker-controlled checksum lengths (s2length). When MAX_DIGEST_LEN exceeds the fixed SUM_LENGTH (16 bytes), an attacker can write out of bounds in the sum2 buffer.

A flaw in rsync causes the client to improperly verify symbolic link destinations when using the `--safe-links` option, allowing path traversal and arbitrary file write outside the intended directory.