# CVE-2026-103501: Apache DataSketches C++ heap buffer overflow in HLL deserialization

Source: https://junglewise.ai/threats/cve-2026-103501-heap-buffer-overflow-in-the-hll-sketch-deserialization-of-apache  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-10. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-103501 · Severity: info · Published 2026-10-10

Apache DataSketches C++ is a library for computing compact statistical summaries of large datasets. A heap buffer overflow in HLL sketch deserialization allows an attacker who can provide crafted sketch data to corrupt heap memory, potentially crashing applications or enabling further code execution exploitation.

Technologies: [Apache DataSketches C++](https://junglewise.ai/threats/technologies/datasketches-c). Vendors: [Apache](https://junglewise.ai/threats/vendors/apache).

## Quick answers

**Is CVE-2026-103501 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-103501 being exploited in the wild.

**How severe is CVE-2026-103501?** Informational severity, published 10 October 2026.

**Which products and versions are affected?** Apache DataSketches C++ 1.0.0-incubating through 5.2.0.

**Is there a fix for CVE-2026-103501?** Yes: fixed in 5.3.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-103501 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-103501?** Check whether you run Apache DataSketches C++ at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 5.3.0

## Technical details

The vulnerability exists in HLL sketch deserialization in LIST mode, where the coupon count from input is used to copy data into a fixed 8-entry buffer without validation. A malicious sketch can write up to 988 bytes past the buffer boundary. Only applications that deserialize HLL sketches from untrusted sources are affected; the attack vector requires providing malformed serialized data.

## Affected products

- Apache DataSketches C++ 1.0.0-incubating through 5.2.0

## Timeline

- 2026-10-10: disclosed

## References

- [https://github.com/](https://github.com/)
- [https://github.com/apache/datasketches-cpp/releases/tag/5.3.0](https://github.com/apache/datasketches-cpp/releases/tag/5.3.0)

## Related threats

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