# What is CVE-2021-3524? > CVE-2021-3524 is a medium-severity flaw (CVSS 6.5) in Ceph from Red Hat, published on 17 May 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 1.6%. If you run an affected version, plan in the vendor’s fix. Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-3524 ## 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:** 23 out of 100 (Low); action: Monitor. Kept up to date as the evidence changes. - **Severity:** Medium (CVSS 6.5 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:** 1.6% (latest exploit-likelihood forecast) - **Published:** 17 May 2021 - **Record last updated:** 7 November 2023 - **Main product:** Ceph from Red Hat - **Affected products:** 4 ## What is CVE-2021-3524? In plain terms It can be attacked from anywhere on the internet without logging in, but a person has to take an action first. If it works, the attacker can change data. ### The official description A flaw was found in the Red Hat Ceph Storage RadosGW (Ceph Object Gateway) in versions before 14.2.21. The vulnerability is related to the injection of HTTP headers via a CORS ExposeHeader tag. The newline character in the ExposeHeader tag in the CORS configuration file generates a header injection in the response when the CORS request is made. In addition, the prior bug fix for CVE-2020-10753 did not account for the use of \r as a header separator, thus a new flaw has been created. ### What kind of flaw is it? - CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') - CWE-20: Improper Input Validation ### 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: No login needed - Does someone have to click: Yes, a person has to take an action - What an attacker gets: Can change data Severity vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N` ## Is CVE-2021-3524 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 1.6%. That can change at any time, which is why we keep watching. Exploit likelihood over the last 7 days: 1.6%, 1.6%, 1.6%, 1.6%, 1.6%, 1.6%, 1.6%. ### Timeline - 17 May 2021: Published - 7 November 2023: Record last updated ### How Precursor Intelligence ranks it CVE-2021-3524 scores **23 out of 100 (Low)**, with the action "Monitor". 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: smaller factor - Threat activity around it: smaller factor 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-2021-3524? The published record lists 4 products. Versions are as published: "before 14.2.21" means every version up to, but not including, 14.2.21. - [Ceph](https://www.precursorintelligence.com/product/redhat/ceph) by [Red Hat](https://www.precursorintelligence.com/vendors/redhat) (Application): before 14.2.21 - [Fedora](https://www.precursorintelligence.com/product/fedoraproject/fedora) by [Fedoraproject](https://www.precursorintelligence.com/vendors/fedoraproject) (Operating system): 32, 33, 34 - [Ceph Storage](https://www.precursorintelligence.com/product/redhat/ceph_storage) by [Red Hat](https://www.precursorintelligence.com/vendors/redhat) (Application): 4.0 - [Debian Linux](https://www.precursorintelligence.com/product/debian/debian_linux) by [Debian](https://www.precursorintelligence.com/vendors/debian) (Operating system): 9.0 ## How do I fix CVE-2021-3524? 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 - [bugzilla.redhat.com](https://bugzilla.redhat.com/show_bug.cgi?id=1951674) (Issue tracking, Patch, Vendor advisory) - [lists.debian.org](https://lists.debian.org/debian-lts-announce/2021/08/msg00013.html) (Mailing list, Third-party advisory) - [lists.debian.org](https://lists.debian.org/debian-lts-announce/2023/10/msg00034.html) - [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FX5ZHI5L7FOHXOSEV3TYBAL66DMLJ7V5/) - [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LPCJN2YDZCBMF4FOJXSTAADKFGEQEO7O/) - [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZRUNDH2TJRZRWL3DCH2PQ6KROWTPQ7AJ/) ## Questions ### What is CVE-2021-3524? CVE-2021-3524 is a medium-severity flaw in Ceph from Red Hat, published on 17 May 2021. It can be attacked from anywhere on the internet without logging in, but a person has to take an action first. If it works, the attacker can change data. ### How serious is CVE-2021-3524? It scores 6.5 out of 10 on the CVSS severity scale, which is medium. Our risk score for CVE-2021-3524 is 23 out of 100, which is Low. Its action is "Monitor". No sign of exploitation and a low forecast. Patch it in your normal update cycle. ### Is CVE-2021-3524 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 1.6%. That can change at any time, which is why we keep watching. ### Which versions does CVE-2021-3524 affect? For Ceph from Red Hat: before 14.2.21. The record lists 4 products in all, each with its versions, under "Who is affected" on this page. ### How do I fix CVE-2021-3524? 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-2021-3524 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