Rsync version 3.4.2 and prior contain a receiver-side out-of-bounds array read vulnerability in recv_files() in receiver.c that allows a malicious rsync server to crash the rsync client process. Attackers can exploit the vulnerability by setting CF_INC_RECURSE in compatibility flags and sending a specially crafted file list where the first sorted entry is not the leading dot directory, followed by a transfer record with ndx=0 and an iflag word without ITEM_TRANSFER, causing the receiver to read 8 bytes before the allocated pointer array and dereference an invalid pointer at an unmapped address, resulting in a deterministic SIGSEGV crash of the rsync client.
Weakness
The product reads data past the end, or before the beginning, of the intended buffer.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Rsync | Samba | * | 3.4.2 (including) |
| Rsync | Ubuntu | devel | * |
| Rsync | Ubuntu | esm-infra-legacy/trusty | * |
| Rsync | Ubuntu | esm-infra-legacy/xenial | * |
| Rsync | Ubuntu | esm-infra/bionic | * |
| Rsync | Ubuntu | esm-infra/focal | * |
| Rsync | Ubuntu | esm-infra/xenial | * |
| Rsync | Ubuntu | jammy | * |
| Rsync | Ubuntu | noble | * |
| Rsync | Ubuntu | questing | * |
| Rsync | Ubuntu | resolute | * |
| Rsync | Ubuntu | upstream | * |
Potential Mitigations
- Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
- When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
- Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.