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CVE-2026-103501: Apache DataSketches: datasketches-cpp: HLL CouponList Deserialization Buffer Overflow allows memory corruption via a crafted sketch

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-10 · updated 2026-10-16
• Weakness: CWE-122

Description

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.

Affected products

• Apache Software Foundation Apache DataSketches: from 1.0.0-incubating through 5.2.0

References

• https://github.com/apache/datasketches-cpp/releases/tag/5.3.0
• https://lists.apache.org/thread/n2oc2j841dzsv4239jjp08of66bo79c5
• http://www.openwall.com/lists/oss-security/2026/10/10/2

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