CVE-2021-36155 — grpc-swift
HIGHCVE-2021-36155 is a high-severity (CVSS 7.5) CWE-770 vulnerability in github.com/grpc/grpc-swift. A fix is available for github.com/grpc/grpc-swift — see the affected versions and patch details below.
Uncontrolled Resource Consumption in LengthPrefixedMessageReader
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-2021-36155 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 377,636 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
github.com/grpc/grpc-swiftReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects SwiftURL packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Affected gRPC Swift clients and servers are vulnerable to uncontrolled resource consumption attacks. Excessive memory may be allocated when parsing messages. This can lead to a denial of service.
Patches
The problem has been fixed in 1.2.0.
Workarounds
No workaround is available. Users must upgrade.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦SwiftURL | github.com/grpc/grpc-swift | all versions | 1.2.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/grpc/grpc-swift, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/grpc/grpc-swift to 1.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-36155 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-2021-36155 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-36155. 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-2021-36155 in your dependencies?
O3 Security finds CVE-2021-36155 across SwiftURL dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.