--- title: "Leaky Vessels: runc Container Escape (CVE-2024-21626)" url: https://erroneo.us/security/briefs/runc-leaky-vessels-container-escape/ description: "runc 1.0.0-rc93 to 1.1.11 leaked a host fd, letting a malicious image or exec escape to the host. Fixed in runc 1.1.12. Not in KEV. Patch this week." type: security-brief section: "Security Digest" date_published: 2024-01-31 date_modified: 2026-10-21 publisher: erroneo.us author: erroneo.us Security Desk verdict: "Patch this week" cves: ["CVE-2024-21626", "CVE-2024-23651", "CVE-2024-23652", "CVE-2024-23653"] severity: "high" exploited: "none-known" kev: false license: All rights reserved. Quote with attribution and a link. --- # Leaky Vessels: runc Container Escape (CVE-2024-21626) **Verdict: Patch this week.** A real container escape, but it needs you to run an attacker-controlled image or a crafted exec; patch runc everywhere promptly, urgently where untrusted images or multi-tenant builds run. - **Who must act:** Anyone running containers on Linux with runc 1.1.11 or earlier, most urgently CI runners, shared build hosts and multi-tenant clusters that run images or Dockerfiles from others. - **Who can relax:** Hosts already on runc 1.1.12 or later, and single-tenant hosts running only trusted, pinned images, which still should patch but on a normal cycle. - **Affected:** runc v1.0.0-rc93 through 1.1.11; BuildKit before 0.12.5; Moby / Docker Engine before 25.0.2 and 24.0.9 - **Fixed:** runc 1.1.12; BuildKit 0.12.5; Moby / Docker Engine 25.0.2 and 24.0.9; containerd 1.6.28 (released alongside) - **CVEs:** CVE-2024-21626, CVE-2024-23651, CVE-2024-23652, CVE-2024-23653 - **CISA KEV:** no · **Exploitation:** No known exploitation ## What to do 1. Check your runc version with `runc --version` (and `docker info` or `containerd --version` on managed nodes) and upgrade to runc 1.1.12 or later. 2. Update Docker Engine to 25.0.2 / 24.0.9 or later and BuildKit to 0.12.5 or later. 3. Patch Kubernetes node images through your provider or distro; managed nodes often bundle runc. 4. Until patched, run only trusted images and keep process.cwd and --cwd set to /. 5. Prioritize CI runners and shared build infrastructure that build or run third-party Dockerfiles. ### How to check if you are affected - Search images and Dockerfiles for WORKDIR or symlinks referencing /proc/self/fd/. - Look for container specs or `runc exec --cwd` values resolving through /proc/self/fd/. - Run Snyk's open-source leaky-vessels static or runtime detectors as a hunting aid. - Check host binaries (for example with your package manager's verify mode) for unexpected modification. ## What happened On January 31, 2024, the runc maintainers published [GHSA-xr7r-f8xq-vfvv](https://github.com/opencontainers/runc/security/advisories/GHSA-xr7r-f8xq-vfvv) (CVE-2024-21626). runc, the low-level runtime underneath Docker, containerd and most Kubernetes nodes, leaked internal file descriptors into the container's init process, including a handle to the host's `/sys/fs/cgroup`. It also did not check that the working directory was still inside the container after `chdir`. Together, that let a container process get a working directory on the host filesystem. The advisory describes four attacks: - **Attack 1 (runc run):** a malicious image sets its working directory to something like `/proc/self/fd/7/`, landing the process in the host's mount namespace. - **Attack 2 (runc exec):** a process already in a container swaps a path used by `runc exec --cwd` for a symlink to the leaked fd. - **Attacks 3a and 3b:** variants that overwrite host binaries, which gives a full escape. Rory McNamara of Snyk found the original issue and named the set ["Leaky Vessels"](https://labs.snyk.io/resources/leaky-vessels-docker-runc-container-breakout-vulnerabilities/), together with three BuildKit bugs disclosed the same day: CVE-2024-23651 (mount cache race), CVE-2024-23652 (arbitrary delete on build-container teardown) and CVE-2024-23653 (gRPC SecurityMode privilege check). Other variants were credited to lifubang and Aleksa Sarai. ## Who is affected runc v1.0.0-rc93 through 1.1.11. The fix is runc 1.1.12. Snyk lists the downstream fixes as BuildKit 0.12.5 and Moby (Docker Engine) 25.0.2 and 24.0.9, with containerd 1.6.28 also released. [NVD](https://nvd.nist.gov/vuln/detail/CVE-2024-21626) rates CVE-2024-21626 at 8.6 (local attack vector, user interaction required). The advisory notes crun and youki do not currently leak useful fds, though they lack runc's new hardening. ## Do you really need to act? Yes, but the urgency depends on who controls your images. Every attack requires either running an attacker-built image or Dockerfile, or an attacker already inside a container plus someone running `runc exec` into it. That makes the highest-risk environments: - CI/CD runners and build services that build arbitrary Dockerfiles from pull requests or customers. - Multi-tenant Kubernetes clusters and platforms that run user-supplied images. - Developer machines that pull and run untrusted images. On a single-tenant host running only your own pinned images, an attacker first needs to compromise your supply chain. Snyk reported finding no evidence of exploitation in its non-exhaustive checks of public Dockerfiles. CVE-2024-21626 is not in the [CISA KEV catalog](https://www.cisa.gov/known-exploited-vulnerabilities-catalog) as of October 21, 2026. Still, container escapes break the main promise of containers, and runc is everywhere, so patch within days, not months. ## What to do now 1. Run `runc --version` on hosts (and check `docker version` for the Engine) and upgrade to runc 1.1.12 or later. 2. Update Docker Engine to 25.0.2 / 24.0.9 or later and BuildKit to 0.12.5 or later. 3. Roll Kubernetes node pools to patched images from your provider or distro. 4. Until patched, run only trusted images and keep `process.cwd` and `--cwd` at `/`, the advisory's workaround for attacks 1 and 2. Attack 3b has no practical workaround besides avoiding `runc exec`. 5. Patch shared build infrastructure first. ## How to tell if you were hit The advisory publishes no formal indicators. Practical hunting: search Dockerfiles and image layers for a `WORKDIR`, working directory or symlink pointing into `/proc/self/fd/`, and executable paths that traverse out of it (for example `/proc/self/fd/7/../../../bin/bash`). Snyk released open-source static and eBPF runtime detectors (leaky-vessels-static-detector and leaky-vessels-runtime-detector) as hunting aids; each hit needs manual review. Verify host binaries against your package manager if you suspect attack 3. ## Timeline - Jan 31, 2024 — runc 1.1.12, BuildKit 0.12.5 and Docker Engine 25.0.2 / 24.0.9 released; advisories published. - Oct 21, 2026 — No in-the-wild exploitation confirmed in the sources reviewed; not in KEV; brief updated. ## Sources 1. [runc — GHSA-xr7r-f8xq-vfvv: Several container breakouts due to internally leaked fds](https://github.com/opencontainers/runc/security/advisories/GHSA-xr7r-f8xq-vfvv) 2. [NVD — CVE-2024-21626](https://nvd.nist.gov/vuln/detail/CVE-2024-21626) 3. [Snyk Labs — Leaky Vessels: Docker and runc container breakout vulnerabilities](https://labs.snyk.io/resources/leaky-vessels-docker-runc-container-breakout-vulnerabilities/) 4. [CISA — Known Exploited Vulnerabilities Catalog](https://www.cisa.gov/known-exploited-vulnerabilities-catalog) --- Source page: https://erroneo.us/security/briefs/runc-leaky-vessels-container-escape/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt