CVE-2021-21249: Post-Auth Unsafe Yaml deserialization

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 3.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-01-15 · updated 2026-06-17
Weakness: CWE-74

Description

OneDev is an all-in-one devops platform. In OneDev before version 4.0.3, there is an issue involving YAML parsing which can lead to post-auth remote code execution. In order to parse and process YAML files, OneDev uses SnakeYaml which by default (when not using `SafeConstructor`) allows the instantiation of arbitrary classes. We can leverage that to run arbitrary code by instantiating classes such as `javax.script.ScriptEngineManager` and using `URLClassLoader` to load the script engine provider, resulting in the instantiation of a user controlled class. For a full example refer to the referenced GHSA. This issue was addressed in 4.0.3 by only allowing certain known classes to be deserialized

Affected products

theonedev onedev: before 4.0.3 — fixed in 4.0.3

How to fix

Upgrade to a fixed version: theonedev onedev 4.0.3. Check the vendor advisory for mitigations.

References

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