CVE-2026-103636 Denial of service in Apache DataSketches
An out-of-bounds read in VarOpt union deserialization allows attackers to cause crashes or expose memory via truncated input.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-103636?
CVE-2026-103636 is a high-severity denial of service vulnerability in Apache DataSketches, published on 10 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Out-of-bounds read in the VarOpt union deserialization of Apache DataSketches C++ (repo: datasketches-cpp).
var_opt_union::deserialize() read the 32-byte preamble of a non-empty union after checking that only 8 bytes were available, so a truncated serialized union could cause a read of up to 24 bytes past the end of the input. For such inputs, the size remaining for the embedded sketch was also computed by an unsigned subtraction that could wrap around, so the embedded sketch's own size checks no longer limited reads to the input. The bytes read can become part of the deserialized union's state. This can cause a crash (denial of service) and could expose adjacent memory contents.
This issue affects Apache DataSketches C++: from 2.0.0-incubating before 5.3.0. Only applications that deserialize VarOpt unions from untrusted sources are affected.
Users are recommended to upgrade to version 5.3.0, which fixes this issue.
Which versions are affected by CVE-2026-103636?
How do I fix CVE-2026-103636?
No fix has been published for CVE-2026-103636 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-103636 being exploited?
There is no known exploitation of CVE-2026-103636 in the wild and no public exploit code.
Sources
Also known as GHSA-9935-w26g-xf2m.