Out-of-bounds Write (CWE-787) in the PEA archive extraction routine (pea.pas, unpea_procedure) of the first-party pea component in PeaZip 11.2.0 and earlier allows an attacker who convinces a victim to open or extract a crafted .pea archive to execute arbitrary code as the user running PeaZip. While decompressing a PCOMPRESS1 stream, the 32-bit compressed-block-size field of the first block (compsize) is read directly from the archive and used without validation as the length of a blockread into the fixed-size global buffers wbuf1/wbuf2 (1,114,112 bytes) and as the bound of the subsequent copy loop. The existing check compsize > WBUFSIZE is applied only to the size of each following block, so the first block escapes it; the same unvalidated value is also used to index wbuf1[compsize], an out-of-bounds read at an attacker-chosen offset. The copy loop additionally copies the requested length instead of the number of bytes actually read, and terminates on equality rather than on an upper bound. Because the project is built without range checking and no archive password, integrity tag or non-default configuration is required, the overflow overwrites adjacent global data; code execution was demonstrated by two independent researchers against the official Linux x86-64 and Windows x64 builds, and the denial-of-service and memory-corruption primitive is cross-platform (Windows, macOS, Linux, BSD).
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.