# What is CVE-2021-43783? > CVE-2021-43783 is a high-severity flaw (CVSS 8.5) in Backstage from Linuxfoundation, published on 29 November 2021. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 1.2%. If you run an affected version, plan in the vendor’s fix. Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-43783 ## At a glance - **Verdict:** Plan it in. No sign of exploitation and a low forecast. Patch it in your normal update cycle. - **Precursor Intelligence risk score:** 47 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes. - **Severity:** High (CVSS 8.5 out of 10) - **Known to be exploited:** No, not on the list of flaws known to be exploited today - **Chance of use in the next 30 days:** 1.2% (latest exploit-likelihood forecast) - **Published:** 29 November 2021 - **Record last updated:** 3 January 2025 - **Main product:** Backstage from Linuxfoundation - **Affected products:** 1 ## What is CVE-2021-43783? In plain terms It can be attacked from anywhere on the internet with an ordinary user account, and nobody has to click anything. If it works, the attacker can change data. ### The official description @backstage/plugin-scaffolder-backend is the backend for the default Backstage software templates. In affected versions a malicious actor with write access to a registered scaffolder template is able to manipulate the template in a way that writes files to arbitrary paths on the scaffolder-backend host instance. This vulnerability can in some situation also be exploited through user input when executing a template, meaning you do not need write access to the templates. This method will not allow the attacker to control the contents of the injected file however, unless the template is also crafted in a specific way that gives control of the file contents. This vulnerability is fixed in version `0.15.14` of the `@backstage/plugin-scaffolder-backend`. This attack is mitigated by restricting access and requiring reviews when registering or modifying scaffolder templates. ### What kind of flaw is it? - CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') ### How an attack on it works - Where an attacker can be: Anywhere on the internet - How hard it is to pull off: Easy: no special conditions - Login needed first: An ordinary user account - Does someone have to click: No, nobody has to do anything - What an attacker gets: Can change data Severity vector: `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:L` ## Is CVE-2021-43783 being exploited? Not that we know of It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 1.2%. That can change at any time, which is why we keep watching. Exploit likelihood over the last 7 days: 1.2%, 1.2%, 1.2%, 1.2%, 1.2%, 1.2%, 1.2%. ### Timeline - 29 November 2021: Published - 3 January 2025: Record last updated ### How Precursor Intelligence ranks it CVE-2021-43783 scores **47 out of 100 (Medium)**, with the action "Plan remediation". Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less: - Evidence it is being exploited: biggest factor - How severe it is: strong factor - How widely exposed it is: key context - Real threat activity around it: key context 85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it. ## Who is affected by CVE-2021-43783? The published record lists 1 product. Versions are as published: "before 0.15.14" means every version up to, but not including, 0.15.14. - [Backstage](https://www.precursorintelligence.com/product/linuxfoundation/backstage) by [Linuxfoundation](https://www.precursorintelligence.com/vendors/linuxfoundation) (Application): before 0.15.14 ## How do I fix CVE-2021-43783? 1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list. 2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisory first in the list. 3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in. 4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood. ### References - [github.com](https://github.com/backstage/backstage/commit/f9352ab606367cd9efc6ff048915c70ed3013b7f) (Patch, Third-party advisory) - [github.com](https://github.com/backstage/backstage/security/advisories/GHSA-mg3m-f475-28hv) (Third-party advisory) ## Questions ### What is CVE-2021-43783? CVE-2021-43783 is a high-severity flaw in Backstage from Linuxfoundation, published on 29 November 2021. It can be attacked from anywhere on the internet with an ordinary user account, and nobody has to click anything. If it works, the attacker can change data. ### How serious is CVE-2021-43783? It scores 8.5 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-43783 is 47 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle. ### Is CVE-2021-43783 being exploited? It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 1.2%. That can change at any time, which is why we keep watching. ### Which versions does CVE-2021-43783 affect? For Backstage from Linuxfoundation: before 0.15.14. ### How do I fix CVE-2021-43783? Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. ## Does CVE-2021-43783 affect you? Precursor Intelligence keeps checking for you: - **Tell us what you run.** Pick your software from a list, or let us work it out from your website. - **We match it to every flaw.** Over 400,000 published flaws, checked against your list. - **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it. - **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools. Start free (no card, nothing to install): https://www.precursorintelligence.com/register Book a demo: https://www.precursorintelligence.com/contact