Apache DataSketches C++: Heap buffer overflow in HLL sketch deserialization
Summary
The HLL sketch deserialization of Apache DataSketches C++ does not check the coupon count of a sketch in LIST mode against the buffer capacity. A crafted sketch can cause a heap buffer overflow of up to 988 bytes, which can corrupt heap memory and crash the application or potentially enable further exploitation. Only applications that deserialize HLL sketches from untrusted sources are affected.
Affected
- Apache DataSketches C++ from 1.0.0-incubating before 5.3.0
- Sources differ on the last affected version: the CVE record and OSV list 5.2.0, PT-2026-109640 lists 5.2.9. Treat all 5.2.x builds as affected.
Fixed in
- Upgrade to Apache DataSketches C++ 5.3.0 or later.
- The PostgreSQL datasketches extension and Rust bindings have moved to the fixed core library version.
Workaround
- Unknown. The CVE record provides no workaround.
- Stop deserializing HLL sketches from untrusted sources until the library is upgraded.
- Validate or reject sketch input at the application boundary.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact total.
- No evidence of exploitation in the wild found. Not listed in KEV.
- No public proof of concept found.
- EPSS about 0.00555.
Our recommendation
- Inventory where datasketches-cpp or its bindings are used, including vendored copies in applications and container images.
- Upgrade to version 5.3.0 where present.
- Until then, do not process HLL sketches from untrusted sources and reject external sketch input.
- Check whether the NVD score of 9.8 has been published and re-verify the record before reporting.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- 5.3.0 release github.com
- OSV entry CVE-2026-103501 osv.dev
- OpenCVE CVE-2026-103501 app.opencve.io
- Apache mailing list thread lists.apache.org
- Openwall oss-security www.openwall.com
- PT-2026-109640 vulners.com
- PostgreSQL extension update PR github.com
- EPSS via Rapid7 record vulners.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 30 Oct 2026, 19:46.
Original description (NVD)
Heap buffer overflow in the HLL sketch deserialization of Apache DataSketches C++ (repo: datasketches-cpp). When deserializing a sketch in LIST mode, from either a byte buffer or a stream, the coupon count was read from the input and used as the number of entries to copy into a fixed buffer of 8 entries, without checking it against the buffer's capacity. A crafted sketch could cause a write of up to 988 bytes past the end of this internal heap buffer. This can corrupt heap memory, causing a crash and potentially enabling further exploitation. This issue affects Apache DataSketches C++: from 1.0.0-incubating before 5.3.0. Only applications that deserialize HLL sketches from untrusted sources are affected. Users are recommended to upgrade to version 5.3.0, which fixes this issue.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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