Out-of-bounds read in the compact Theta sketch deserialization of Apache DataSketches C++ (repo…

Why it is Amber

• CVSS 9.1 critical
• Remotely exploitable without logging in

References

• https://github.com/apache/datasketches-cpp/releases/tag/5.3.0
• https://lists.apache.org/thread/15b86y9jstco39kzppjw7l5kvhjvwqvv
• http://www.openwall.com/lists/oss-security/2026/10/10/5

Original description

Out-of-bounds read in the compact Theta sketch deserialization of Apache DataSketches C++ (repo: datasketches-cpp). compact_theta_sketch::deserialize() and wrapped_compact_theta_sketch::wrap() read header fields before checking that the input was long enough. For the compressed format, the size check could be defeated by a 32-bit overflow, and two header fields that control decoding were not validated; this also affected deserialization from a stream. A crafted or truncated sketch could cause a read past the end of the input. In the compressed case the over-read can be large, and the bytes read can become part of the deserialized sketch. This can cause a crash (denial of service) and could expose adjacent memory contents. This issue affects Apache DataSketches C++: from 3.1.0 before 5.3.0. Only applications that deserialize Theta sketches from untrusted sources are affected. Users are recommended to upgrade to version 5.3.0, which fixes this issue.