youki container escape via "masked path" abuse due to mount race conditions

### Impact ### youki utilizes bind mounting the container's `/dev/null` as a file mask. When performing this operation, the initial validation of the source `/dev/null` was insufficient. Specifically, we initially failed to verify whether `/dev/null` was genuinely present. However, we did perform validation to ensure that the `/dev/null` path existed within the container, including checking for symbolic links. Additionally, there was a vulnerability in the timing between validation and the actual mount operation. As a result, by replacing `/dev/null` with a symbolic link, we can bind-mount arbitrary files from the host system. This is a different project, but the core logic is similar to the CVE in runc. Issues were identified in runc, and verification was also conducted in youki to confirm the problems. https://github.com/opencontainers/runc/security/advisories/GHSA-9493-h29p-rfm2 ### Credits Thanks to Lei Wang (@ssst0n3 from Huawei) for finding and reporting the original runc's vulnerability (Attack 1), and Li Fubang (@lifubang from acmcoder.com, CIIC) for discovering another attack vector in runc (Attack 2) based on @ssst0n3's initial findings. Also, @cyphar helped youki in finding the problem.

Source published

5 Nov 2025 18:44:18 UTC

Source modified

15 Nov 2025 02:25:02 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS_V4 · CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

Publisher rating · HIGH