CVE-2021-33194 is a high-severity (CVSS 7.5) CWE-835 vulnerability in golang.org/x/net. A fix is available for golang.org/x/net — see the affected versions and patch details below.
golang.org/x/net/html Infinite Loop vulnerability
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-2021-33194 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 379,145 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
golang.org/x/netReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
golang.org/x/net before v0.0.0-20210520170846-37e1c6afe023 allows attackers to cause a denial of service (infinite loop) via crafted ParseFragment input.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | golang.org/x/net | all versions | 0.0.0-20210520170846-37e1c6afe023go get golang.org/x/net@v0.0.0-20210520170846-37e1c6afe023 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for golang.org/x/net, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update golang.org/x/net to 0.0.0-20210520170846-37e1c6afe023 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33194 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-33194 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-33194. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Red Hat Developer Tools go-toolset-1.14-golang not affected because the vulnerable code is not shipped. This vulnerability within golang and buildah shipped with RHEL-7 are out of support scope. For more information on Red Hat's support scope, visit: https://access.redhat.com/support/policy/updates/errata For RHEL-8's…
| Product | Fixed in | Advisory |
|---|---|---|
| OpenShift Logging 5.3 | openshift-logging/elasticsearch-proxy-rhel8:v1.0.0-44 | RHSA-2021:4627 |
| Red Hat OpenShift Container Platform 4.8 | openshift4/ose-cluster-node-tuning-operator:v4.8.0-202107091725.p0.git.6be3f67.assembly.stream | RHSA-2021:2438 |
| Red Hat OpenShift Container Platform 4.9 | openshift4/ose-oauth-proxy:v4.9.0-202109302016.p0.git.9ea1ebc.assembly.stream | RHSA-2021:3759 |
Frequently Asked Questions
Is CVE-2021-33194 in your dependencies?
O3 Security finds CVE-2021-33194 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.