# CVE-2026-103634: Out-of-bounds read and write in the Count-Min sketch deserialization of Apache DataSketches C++ (repo: datasketches-cpp).


- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 22 Oct 2026
- **Updated:** 26 Oct 2026
- **Also known as:** GHSA-8255-5x7v-6cgv

## What is CVE-2026-103634?

CVE-2026-103634 is a medium-severity vulnerability in Apache DataSketches, published on 22 Oct 2026. 

### Official description

Out-of-bounds read and write in the Count-Min sketch deserialization of Apache DataSketches C++ (repo: datasketches-cpp).

count_min_sketch::deserialize() did not include the preamble in its input size check, so a truncated sketch could cause a read of up to 16 bytes past the end of the input. In addition, the table size was computed from the serialized number of buckets and number of hash functions in 32-bit arithmetic. A crafted sketch could make it wrap to zero, so that the sketch deserialized with an empty table, and later updates and estimate queries read and wrote outside the heap allocation. This can corrupt heap memory, causing a crash and potentially enabling further exploitation.

This issue affects Apache DataSketches C++: from 4.1.0 before 5.3.0. Only applications that deserialize Count-Min sketches from untrusted sources are affected.

Users are recommended to upgrade to version 5.3.0, which fixes this issue.

Weakness: CWE-787 (Out-of-bounds Write), CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-103634?


## How do I fix CVE-2026-103634?

No fix has been published for CVE-2026-103634 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-103634 being exploited?

There is no known exploitation of CVE-2026-103634 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-103634 and fix it if it is affected.

What it is: CVE-2026-103634 is a medium-severity vulnerability in Apache DataSketches, published on 22 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-103634 in the wild and no public exploit code.

Affected product: Apache DataSketches. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-103634/ (Markdown: https://insights.sbomify.com/CVE-2026-103634/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103634
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103634
- OSV: https://osv.dev/vulnerability/CVE-2026-103634

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103634/
Summaries are generated and may contain mistakes; the official description above is the record.