# CVE-2026-103635: Apache DataSketches C++ out-of-bounds read in Theta sketch deserialization

Source: https://junglewise.ai/threats/cve-2026-103635-out-of-bounds-read-in-the-compact-theta-sketch-deserialization  
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-2026-103635 · Severity: info · Published 2026-10-10

Apache DataSketches C++ is a library for probabilistic data analysis used in analytics and big data applications. The library's Theta sketch deserialization functions fail to properly validate input buffer size before reading header fields, allowing a crafted sketch to cause out-of-bounds memory reads. An attacker can trigger a crash (denial of service) or potentially expose adjacent memory contents by providing a malformed or truncated sketch to an application that deserializes untrusted data.

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

## Quick answers

**Is CVE-2026-103635 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-103635 being exploited in the wild.

**How severe is CVE-2026-103635?** Informational severity, published 10 October 2026.

**Which products and versions are affected?** Apache DataSketches C++ 3.1.0 through 5.2.0.

**Is there a fix for CVE-2026-103635?** Yes: fixed in 5.3.0. Until then: Only applications that deserialize Theta sketches from untrusted sources are affected; applications that only process sketches from trusted internal sources are not at risk.</anigation>
<parameter name="timeline">[{"kind":"disclosed","at":"2026-10-10"}] Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-103635 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-103635?** 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

Only applications that deserialize Theta sketches from untrusted sources are affected; applications that only process sketches from trusted internal sources are not at risk.</anigation>
<parameter name="timeline">[{"kind":"disclosed","at":"2026-10-10"}]

## Technical details

The compact_theta_sketch::deserialize() and wrapped_compact_theta_sketch::wrap() functions read header fields before validating that the input buffer is sufficiently long. In the compressed format, a 32-bit integer overflow can defeat the size check, and two unvalidated header fields control decoding logic. A crafted input causes a read past the buffer boundary; in compressed cases, over-reads can be large and read bytes may be incorporated into the deserialized sketch, leaking adjacent heap memory.

## Affected products

- Apache DataSketches C++ 3.1.0 through 5.2.0

## 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

- [Apache DataSketches C++ out-of-bounds read and write in Count-Min deserialization](https://junglewise.ai/threats/cve-2026-103634-out-of-bounds-read-and-write-in-the-count-min-sketch)
- [Apache DataSketches C++ out-of-bounds read in VarOpt union deserialization](https://junglewise.ai/threats/cve-2026-103636-out-of-bounds-read-in-the-varopt-union-deserialization-of-apache)
- [Apache DataSketches C++ out-of-bounds read/write in CPC deserialization](https://junglewise.ai/threats/cve-2026-103513-out-of-bounds-read-and-write-in-the-cpc-sketch-deserialization)
- [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)