CVE-2026-103636 Apache Software Foundation CVE debrief

Who should care

Defenders of applications using Apache DataSketches C++ should assess exposure, especially if deserializing VarOpt unions from untrusted sources. This includes developers and security teams responsible for maintaining and securing applications that utilize Apache DataSketches C++.

Why it matters

CVE-2026-103636 is an out-of-bounds read issue in Apache DataSketches C++'s VarOpt union deserialization. Defenders should assess exposure in applications deserializing from untrusted sources, prioritize upgrading to version 5.3.0, and monitor for denial-of-service attempts. Evidence from official sources supports these defensive actions.

• Denial of service (crash) is possible when deserializing truncated VarOpt unions
• Potential exposure of adjacent memory contents when deserializing untrusted input
• Verification of affected versions and upgrade to 5.3.0 is necessary to mitigate the issue
• Assessment of application exposure based on input sources is required

Technical summary

The VarOpt union deserialization in Apache DataSketches C++ contains an out-of-bounds read vulnerability. When deserializing a truncated VarOpt union, the function reads up to 24 bytes past the end of the input. This can cause a crash (denial of service) and potentially expose adjacent memory contents. The issue affects Apache DataSketches C++ versions from 2.0.0-incubating to before 5.3.0. Affected applications are those that deserialize VarOpt unions from untrusted sources. Users should assess exposure and prioritize upgrading to version 5.3.0.

Defensive priority

Upgrade to version 5.3.0, assess exposure in applications deserializing VarOpt unions from untrusted sources, and monitor for potential denial-of-service attempts.

Recommended defensive actions

• Upgrade to Apache DataSketches C++ version 5.3.0
• Assess exposure in applications deserializing VarOpt unions from untrusted sources
• Monitor for potential denial-of-service attempts
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD entry provide details on the out-of-bounds read issue in Apache DataSketches C++. The issue is caused by improper deserialization of VarOpt unions, which can lead to a crash and potential exposure of adjacent memory contents.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.