# CVE-2026-103634: Apache DataSketches C++ out-of-bounds read and write in Count-Min deserialization

Source: https://junglewise.ai/threats/cve-2026-103634-out-of-bounds-read-and-write-in-the-count-min-sketch  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-22. Updated: 2026-10-22  
License: CC BY 4.0 with a link back

CVE-2026-103634 · Severity: info · Published 2026-10-22

Apache DataSketches C++ is a library for efficient approximate data analysis. The Count-Min sketch deserialization function contains an out-of-bounds memory access vulnerability that could allow an attacker to corrupt heap memory by deserializing a malicious sketch file, potentially causing crashes or enabling further exploitation.

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

## Quick answers

**Is CVE-2026-103634 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-103634 being exploited in the wild.

**How severe is CVE-2026-103634?** Informational severity, published 22 October 2026.

**Which products and versions are affected?** Apache DataSketches C++ 4.1.0 through 5.2.0.

**Is there a fix for CVE-2026-103634?** Yes: fixed in 5.3.0. Until then: Applications should only deserialize Count-Min sketches from trusted sources until upgrading to version 5.3.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-103634 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-103634?** 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

Applications should only deserialize Count-Min sketches from trusted sources until upgrading to version 5.3.0.

## Technical details

The count_min_sketch::deserialize() function fails to include the preamble in its input size check, allowing truncated sketches to read up to 16 bytes past the buffer end. Additionally, table size computation uses 32-bit arithmetic that can wrap to zero when given a crafted sketch, causing subsequent updates and queries to read and write outside heap allocation. The vulnerability affects only applications deserializing sketches from untrusted sources and is fixed in version 5.3.0.

## Affected products

- Apache DataSketches C++ 4.1.0 through 5.2.0

## Timeline

- 2026-10-22: disclosed: Public disclosure date based on NVD publication
- 2026-10-08: patched: Fixed in version 5.3.0 released on October 8, 2026

## 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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- [Apache DataSketches C++ out-of-bounds read in Theta sketch deserialization](https://junglewise.ai/threats/cve-2026-103635-out-of-bounds-read-in-the-compact-theta-sketch-deserialization)
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- [Apache DataSketches C++ heap buffer overflow in HLL deserialization](https://junglewise.ai/threats/cve-2026-103501-heap-buffer-overflow-in-the-hll-sketch-deserialization-of-apache)