CVE-2026-33524 is a high-severity (CVSS 7.5) CWE-789 vulnerability in io.github.ndsev:zserio-runtime. A fix is available for io.github.ndsev:zserio-runtime — see the affected versions and patch details below.
Zserio: Integer Overflow in BitStreamReader and Unbounded Memory Allocation in Deserialization
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-33524.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-33524 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
io.github.ndsev:zserio-runtimeReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Unbounded Memory Allocation (all platforms)
A crafted payload as small as 4-5 bytes can force memory allocations of up to 16 GB, crashing any process with an OOM error (Denial of Service).
Affected code (C++):
cpp/runtime/src/zserio/Array.h(line 1029) —m_rawArray.reserve(readLength)with uncheckedreadLengthcpp/runtime/src/zserio/BitStreamReader.h(lines 249, 281) —value.reserve(len)with uncheckedlen
Affected code (Java):
java/runtime/src/zserio/runtime/array/Array.java(line 271) —rawArray.reset(readSize)→new int[readSize]java/runtime/src/zserio/runtime/io/ByteArrayBitStreamReader.java(line 245) —new byte[length]
Proof of Concept
Memory Allocation DoS (verified on 64-bit)
| Payload | Claimed Size | Allocated | Amplification |
|---|---|---|---|
| 4 bytes | 100,000,000 | 762 MB | ~200 million x |
| 5 bytes | 2,147,483,647 | ~16 GB | system crash |
The full PoC source code and Docker build files are available upon request.
Impact
zserio is the serialization framework underlying the NDS (Navigation Data Standard), used by 43 member companies including Toyota, BMW, Volkswagen, Mercedes-Benz, and others. According to the Eclipse zserio project:
"Zserio serialized data is used in millions of deployments in cars on the road"
Attack vectors include NDS.Live cloud map updates, map data supply chain compromise, and backend data processing pipelines. On 32-bit automotive ECUs, this could affect ADAS functionality.
Suggested Fix
For all runtimes: Validate varsize against stream size
if (claimedSize > remainingBytesInStream) {
throw error("varsize claims more data than available in stream");
}
Disclosure Timeline
- 2026-03-08: Reported to Woven by Toyota PSIRT (go-zserio)
- 2026-03-10: Reported to ndsev/zserio maintainers via GitHub Security Advisory
- 2026-03-23: Split off overflow vulnerability to own report
- 90-day coordinated disclosure timeline
A patch for this issue is available at https://github.com/ndsev/zserio/releases/tag/v2.18.1.
Reporter
Ryuji Yasukochi ([email protected])
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.github.ndsev:zserio-runtime | all versions | 2.18.1io.github.ndsev:zserio-runtime:2.18.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.github.ndsev:zserio-runtime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.github.ndsev:zserio-runtime to 2.18.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33524 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-33524 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-33524. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-33524 in your dependencies?
O3 Security finds CVE-2026-33524 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.