rsync vulnerabilities

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.

A flaw in rsync allows an attacker to manipulate the checksum length (s2length) during file checksum comparison, causing a comparison with uninitialized memory and leaking one byte of stack data at a time.

The daemon in rsync versions 3.1.2 and 3.1.3-development before 2017-12-03 does not check fnamecmp filenames in the daemon_filter_list data structure and does not apply the sanitize_paths protection mechanism to pathnames found in 'xname follows' strings. This allows remote attackers to bypass intended access restrictions.

Rsync 3.1.3-development before 2017-10-24 mishandles archaic checksums, which makes it easier for remote attackers to bypass intended access restrictions.

rsync daemon versions 2.0.0 before 3.5.0 contain a denial of service vulnerability that allows unauthenticated remote attackers to exhaust daemon connection slots by stalling the handshake process before or after module selection without triggering the I/O timeout. Attackers can open many simultaneous connections and trickle data at the minimum rate to avoid timeout, or stall entirely before module selection where no timeout applies, consuming all available connection slots and denying service to legitimate clients.

rsync versions 3.1.0 before 3.5.0 contain an authorization bypass in auth users directive parsing. The auth users parser uses comma-only tokenization when splitting the user list, which fails to correctly handle entries of the form @Group Name where the group name contains a space. The space within the group name causes the parser to split the entry at the space boundary, discarding the deny rule associated with the group. An authenticated user whose username or group membership would be denied by an @Group Name auth users entry can connect to a restricted module because the deny rule is silently discarded during parsing.

rsync versions 3.2.5 before 3.5.0 contain a heap out-of-bounds write vulnerability that allows remote unauthenticated attackers to write one attacker-controlled byte past the end of a heap allocation by supplying a crafted files-from entry. Attackers can trigger the vulnerability against a read-only rsync daemon module by providing a files-from entry containing both an interior and trailing backslash, causing the add_implied_include() function to under-count the trailing backslash when sizing the destination buffer.

rsync versions 2.3.3 before 3.5.0 contain a path traversal vulnerability that allows a malicious sender to escape the module root by exploiting symlinks within the module file tree when using --partial-dir or --backup-dir options. Attackers with write access to place a symlink under the module root, or who can exploit a pre-existing trusted symlink, can direct file writes to locations outside the intended module root, achieving arbitrary file write relative to the module root parent.

rsync versions 3.0.0 through before 3.5.0 contain a null pointer dereference vulnerability in the daemon child process. A remote attacker can send a file list whose first entry is a dot entry not typed as a directory, causing an invalid pointer dereference that terminates the client connection.

rsync version 3.2.3 before 3.5.0 contains an out-of-bounds write in parse_size_arg() where the return value of snprintf() is used directly as an index into a .bss-segment array without bounds checking. This can corrupt .bss memory.

rsync versions 3.0.1 before 3.5.0 contain an out-of-bounds write vulnerability in the read_args() function that allows a malicious sender to corrupt adjacent heap memory by sending a crafted argument list. When the argument count causes the argv allocation to be exactly full, the trailing NULL terminator is written one slot beyond the allocation boundary, corrupting adjacent heap memory.

rsync versions 3.4.2 before 3.5.0 contain a denial of service vulnerability that allows a remote sender to exhaust system resources by specifying the --zt short alias for --compress-threads, which bypasses the refuse options directive's string matching on long option names. Attackers can specify --zt=N with a large value to spawn an unbounded number of Zstandard worker threads on the receiver, exhausting available thread and memory resources.

Rsync before version 3.5.0 contains an algorithmic complexity vulnerability in the hash_search() function that allows a remote attacker to cause a denial of service by delivering a carefully constructed file list. A sender can exploit the quadratic-time worst-case behavior in hash lookups to exhaust receiver CPU resources with a modest number of crafted entries, causing a sustained denial of service.

rsync 3.1.0 before 3.5.0 contains an access control bypass vulnerability that allows remote attackers to circumvent hosts deny rules by inducing DNS resolution failures during hostname-based access control evaluation. When a DNS lookup for a hostname-based deny rule fails, the daemon skips the rule rather than defaulting to a deny decision, enabling attackers who can trigger DNS failures to bypass module-level IP access controls and gain unauthorized access to restricted module file trees.

rsync before 3.5.0 contains a symlink following vulnerability that allows local attackers to overwrite arbitrary files by placing a symlink at a predictable output path such as --log-file, --write-batch, or daemon-mode log and statistics paths. Attackers can exploit rsync's failure to reject symlinks during ancillary file writes to redirect output to arbitrary filesystem locations, achieving local privilege escalation on installations where rsync runs with elevated privileges such as setuid or privileged daemon configurations.

rsync before 3.5.0 contains an arbitrary file read vulnerability that allows attackers to read files accessible to the rsync daemon process by exploiting symlink following in input configuration file handling including --files-from, --password-file, and filter merge files. Attackers can place a symlink at a predictable --files-from or --password-file path, or supply a --files-from path that escapes the daemon module root, to read arbitrary files accessible to the rsync process.

rsync before 3.5.0 contains a symlink race condition vulnerability in the sender's directory scanning logic that allows attackers to cause the sender to enumerate and transfer files outside the module root's intended subtree. Attackers who can create or manipulate symlinks in a path component of the scanned tree can replace a symlink with a directory entry pointing outside the module root between the lstat() call and the subsequent opendir() call, exposing files beyond the intended root in both daemon-mode and non-daemon sender-side scanning.

rsync before 3.5.0 contains a symlink race condition vulnerability in the --remove-source-files feature that allows attackers with symlink creation access to cause arbitrary file deletion. Attackers can atomically substitute a symlink for a source file between transfer completion and the unlink() call, causing rsync to delete the symlink target rather than the intended source file.

rsync before 3.5.0 contains a symlink race condition vulnerability that allows local attackers to cause rsync to apply arbitrary ACLs or extended attributes to unintended files by substituting a symlink at a predictable destination path between the file write and the subsequent acl_set_file() or lsetxattr() call. Attackers can exploit this timing window to redirect ACL and xattr application through a crafted symlink to files outside the intended destination tree, potentially granting elevated permissions and enabling local privilege escalation.

rsync before 3.5.0 contains a privilege confusion vulnerability in the name-converter subprocess uid/gid mapping that allows local attackers to cause transferred files to be owned by root by influencing name-converter responses to return empty values. rsync incorrectly interprets empty responses as successful resolution to uid/gid 0 (root), leading to root ownership assignments.

rsync before 3.5.0 contains a symlink race condition vulnerability in the sender's source tree traversal that allows an attacker who can manipulate a parent directory of the source tree to redirect file reads to unintended paths. Attackers can atomically replace a parent directory component with a symlink pointing outside the source root between path resolution and file open operations to disclose file contents outside the intended transfer root.

rsync before 3.5.0 contains a time-of-check to time-of-use (TOCTOU) race condition vulnerability in the non-daemon receiver's destination directory handling that allows an attacker who can manipulate destination path parent components to redirect file writes to unintended locations. Attackers can substitute a symlink for a component of the destination path between the path resolution and chdir() call, causing the receiver's working directory to be established outside the intended destination tree so that subsequent relative-path file writes land in unintended filesystem locations.

rsync before 3.5.0 contains an arbitrary file write vulnerability that allows attackers to write files outside the intended destination tree by specifying an absolute path via --temp-dir or --link-dest options. The rename-confinement logic is bypassed when these options resolve to paths outside the destination tree, enabling attacker-controlled values to write files to arbitrary locations accessible to the rsync process.

rsync before 3.5.0 contains a path confinement bypass vulnerability that allows remote clients to escape the intended inner-module root confinement by constructing paths that resolve outside the chroot boundary when the module root contains a /./ boundary marker. Attackers can exploit improper handling of the /./ notation or forge delta-basis transfers referencing xname paths that cross the /./ boundary to gain unauthorized read or write access to files outside the module's subtree.

rsync before 3.5.0 contains an out-of-bounds read vulnerability in the sender-side block matching logic that allows a malicious receiver to trigger memory access before the start of an allocated buffer by sending a crafted checksum block with a length of zero. Attackers can send a specially crafted checksum set containing a zero-length block to cause a negative offset calculation during delta computation, resulting in an out-of-bounds read of file data buffer memory on the sender side.

rsync before 3.5.0 contains an improper path handling vulnerability that allows a malicious sender to expand the scope of --delete operations beyond the intended destination subtree. Attackers can exploit multiple variants to cause the receiver to delete files outside the authorized destination directory.

rsync before 3.5.0 contains a newline injection vulnerability in the name-converter uid/gid mapping interface that allows local attackers to forge protocol messages by creating user or group names containing newline characters. Attackers can inject malicious newline characters to corrupt uid/gid mapping logic.

rsync before 3.5.0 contains a filter rule bypass vulnerability that allows authenticated clients to override module-level filter restrictions by supplying malicious --filter merge file directives. Attackers can inject client-side merge file directives to introduce rules that supersede daemon module-level restrictions, gaining access to files the module filter was intended to exclude.

rsync before 3.5.0 contains a path traversal vulnerability that allows remote clients to access files outside the intended module root when use chroot is disabled and the module root path or a component of it is a symlink. The daemon calls chdir() to the module root at session initialization without resolving symlinks via realpath() or equivalent, causing subsequent relative-path operations to reference files relative to the symlink target rather than the intended module root, enabling unauthorized file access.

rsync before 3.5.0 contains a time-of-check to time-of-use (TOCTOU) race condition vulnerability in the rrsync restricted shell wrapper that allows authenticated clients to escape enforced directory restrictions by substituting a symlink for a path component after validation but before transfer processing. Attackers can additionally leverage unrestricted flags such as --copy-unsafe-links, -D, and --log-file through rrsync to read or write files outside the permitted directory subtree.

Rsync before version 3.4.3 contains a TOCTOU race condition in daemon file handling, allowing attackers to redirect file writes outside intended directories by replacing parent directory components with symbolic links. Attackers with write access to a module path can exploit this to create or overwrite arbitrary files, potentially modifying sensitive system files and achieving privilege escalation when the daemon runs with elevated privileges. This vulnerability can only be triggered if the chroot setting is false.

Rsync versions before 3.4.3 have an off-by-one stack write vulnerability in establish_proxy_connection(). A network attacker can corrupt stack memory by sending a malformed HTTP proxy response, writing a null byte out of bounds.

In rsync version 3.4.2 and prior, a receiver-side out-of-bounds array read vulnerability exists in recv_files() in receiver.c. A malicious rsync server can crash the rsync client by sending a specially crafted file list, causing a deterministic SIGSEGV.

Rsync version 3.4.2 and prior contain symlink race condition vulnerabilities in path-based system calls including chmod, lchown, utimes, rename, unlink, mkdir, symlink, mknod, link, rmdir, and lstat that allow local attackers to redirect operations to files outside the exported rsync module. Attackers with local filesystem access can exploit the timing window between path resolution and syscall execution by swapping symlinks to apply sender-supplied permissions, ownership, timestamps, or filenames to arbitrary files outside the intended module boundary on rsync daemons configured with 'use chroot = no'.

Rsync version 3.4.2 and prior contain an integer overflow vulnerability in the compressed-token decoder where a 32-bit signed counter is not checked for overflow. A malicious sender can trigger an overflow that causes the receiver process to read and return data from outside the intended buffer bounds. Attackers can disclose process memory contents including environment variables, passwords, heap and stack data, and library memory pointers, significantly reducing ASLR effectiveness.

Rsync version 3.4.2 and prior contain an authorization bypass vulnerability in the rsync daemon's hostname-based access control list enforcement when configured with chroot. Attackers can bypass hostname-based deny rules by controlling the PTR record for their source IP address, allowing connections from hostnames that administrators intended to deny when reverse DNS resolution fails and defaults to UNKNOWN.

A vulnerability in rsync versions 3.0.1 through 3.4.1 involves the receive_xattr function using an untrusted length value during a qsort call, leading to a use-after-free in the receiver. The victim must run rsync with the -X (--xattrs) option to be vulnerable.

A race condition was found in rsync's handling of symbolic links. By default, rsync skips symbolic links, but an attacker can replace a regular file with a symbolic link at the right moment to bypass this behavior and traverse symbolic links.

A path traversal vulnerability was found in rsync, caused by the `--inc-recursive` option (enabled by default for many clients and can be forced by the server). Insufficient symlink verification combined with per-file-list deduplication checks allows a server to write files outside the client's intended destination directory.

A flaw was found in rsync that could allow a server to enumerate the contents of an arbitrary file from the client's machine. The issue occurs during file copy from client to server when the server sends checksums of local data for comparison. An attacker can send specially crafted checksum values and reconstruct the data byte-by-byte based on client responses.

The rsync command before version 2.3.1 may inadvertently change the permissions of the client's working directory to the permissions of the directory being transferred.