CVE-2026-103636: Apache DataSketches: datasketches-cpp: Out-of-bounds read in VarOpt union deserialization allows denial of service via a truncated sketch
Out-of-bounds read in the VarOpt union deserialization of Apache DataSketches C++ (repo: datasketches-cpp).
varoptunion::deserialize() read the 32-byte preamble of a non-empty union after checking that only 8 bytes were available, so a truncated serialized union could cause a read of up to 24 bytes past the end of the input. For such inputs, the size remaining for the embedded sketch was also computed by an unsigned subtraction that could wrap around, so the embedded sketch's own size checks no longer limited reads to the input. The bytes read can become part of the deserialized union's state. This can cause a crash (denial of service) and could expose adjacent memory contents.
This issue affects Apache DataSketches C++: from 2.0.0-incubating before 5.3.0. Only applications that deserialize VarOpt unions from untrusted sources are affected.
Users are recommended to upgrade to version 5.3.0, which fixes this issue.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Apache DataSketches C++ (datasketches-cpp)to a version that resolves this vulnerability.Fixed in 5.3.0
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Only applications using affected Apache DataSketches C++ versions that deserialize VarOpt unions from untrusted sources are affected. The affected range is from 2.0.0-incubating before 5.3.0.
What does an attacker need to trigger the flaw?
An attacker needs to supply a truncated serialized non-empty VarOpt union to an application that passes untrusted input to var_opt_union::deserialize(). No other prerequisite is specified.
What is the impact of successful exploitation?
Malformed input can cause reads past the end of the provided buffer, which can crash the application and cause denial of service. Adjacent memory contents may also be exposed, and bytes read beyond the input can become part of the deserialized union state.
What should teams do if they use this deserialization path?
Upgrade Apache DataSketches C++ to version 5.3.0, which fixes the issue. Until upgrading, avoid deserializing VarOpt unions from untrusted sources.