# CVE-2021-0244: Junos OS: A race condition in the storm control profile may allow an attacker to cause a Denial of Service condition > A race condition in Junos OS storm control allows attackers to bypass protections and cause denial of service, particularly in Virtual Chassis configurations. - **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** A user has to click or open something - **Fix available:** No - **Published:** 22 Apr 2021 - **Updated:** 16 Sep 2024 - **Also known as:** GHSA-6w22-mmhg-hxh2 ## What is CVE-2021-0244? CVE-2021-0244 is a high-severity vulnerability in Juniper Junos, published on 22 Apr 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link. ### Official description A signal handler race condition exists in the Layer 2 Address Learning Daemon (L2ALD) of Juniper Networks Junos OS due to the absence of a specific protection mechanism to avoid a race condition which may allow an attacker to bypass the storm-control feature on devices. This issue is a corner case and only occurs during specific actions taken by an administrator of a device under certain specifics actions which triggers the event. The event occurs less frequently on devices which are not configured with Virtual Chassis configurations, and more frequently on devices configured in Virtual Chassis configurations. This issue is not specific to any particular Junos OS platform. An Indicator of Compromise (IoC) may be seen by reviewing log files for the following error message seen by executing the following show statement: show log messages | grep storm Result to look for: /kernel: GENCFG: op 58 (Storm Control Blob) failed; err 1 (Unknown) This issue affects: Juniper Networks Junos OS: 14.1X53 versions prior to 14.1X53-D49 on EX Series; 15.1 versions prior to 15.1R7-S6; 15.1X49 versions prior to 15.1X49-D191, 15.1X49-D200 on SRX Series; 16.1 versions prior to 16.1R7-S7; 16.2 versions prior to 16.2R2-S11, 16.2R3; 17.1 versions prior to 17.1R2-S11, 17.1R3; 17.2 versions prior to 17.2R2-S8, 17.2R3-S3; 17.3 versions prior to 17.3R2-S5, 17.3R3-S7; 17.4 versions prior to 17.4R2-S9, 17.4R3; 18.1 versions prior to 18.1R3-S5; 18.2 versions prior to 18.2R2-S6, 18.2R3; 18.3 versions prior to 18.3R1-S7, 18.3R2-S3, 18.3R3; 18.4 versions prior to 18.4R1-S5, 18.4R2; 19.1 versions prior to 19.1R1-S4, 19.1R2. Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) ## Which versions are affected by CVE-2021-0244? It affects 1 product. Products: Juniper Junos. ## How do I fix CVE-2021-0244? No fix has been published for CVE-2021-0244 yet. Limit exposure of the affected software until one is available. ## Is CVE-2021-0244 being exploited? There is no known exploitation of CVE-2021-0244 in the wild and no public exploit code. ## Other vulnerabilities in Juniper Junos - [CVE-2023-36845](https://insights.sbomify.com/CVE-2023-36845/): Juniper Junos OS EX Series and SRX Series PHP External Variable Modification (critical 9.8, exploited in the wild) - [CVE-2020-1631](https://insights.sbomify.com/CVE-2020-1631/): Juniper Junos OS Path Traversal (high 8.8, exploited in the wild) - [CVE-2025-21590](https://insights.sbomify.com/CVE-2025-21590/): Juniper Junos OS Improper Isolation or Compartmentalization (medium 6.7, exploited in the wild) - [CVE-2023-36851](https://insights.sbomify.com/CVE-2023-36851/): Juniper Junos OS SRX Series Missing Authentication for Critical Function (medium 5.3, exploited in the wild) - [CVE-2023-36844](https://insights.sbomify.com/CVE-2023-36844/): Juniper Junos OS EX Series PHP External Variable Modification (medium 5.3, exploited in the wild) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2021-0244 and fix it if it is affected. What it is: CVE-2021-0244 is a high-severity vulnerability in Juniper Junos, published on 22 Apr 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link. Exploitation: There is no known exploitation of CVE-2021-0244 in the wild and no public exploit code. Affected product: Juniper Junos. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2021-0244/ (Markdown: https://insights.sbomify.com/CVE-2021-0244/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2021-0244 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-0244 - OSV: https://osv.dev/vulnerability/CVE-2021-0244 --- From sbomify Insights: https://insights.sbomify.com/CVE-2021-0244/ Summaries are generated and may contain mistakes; the official description above is the record.