There exists an out of bounds read/write in LibJXL versions prior to commit 9cc451b91b74ba470fd72bd48c121e9f33d24c99. The JPEG decoder used by the JPEG XL encoder when doing JPEG recompression (i.e. if using JxlEncoderAddJPEGFrame on untrusted input) does not properly check bounds in the presence of incomplete codes. This could lead to an out-of-bounds write. In jpegli which is released as part of the same project, the same vulnerability is present. However, the relevant buffer is part of a bigger structure, and the code makes no assumptions on the values that could be overwritten. The issue could however cause jpegli to read uninitialised memory, or addresses of functions.
Weakness
The product reads data past the end, or before the beginning, of the intended buffer.
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.
References