# What is CVE-2021-41773?

> CVE-2021-41773 is a high-severity flaw (CVSS 7.5) in HTTP Server from Apache, published on 5 October 2021. It is on the list of flaws known to be exploited, so criminals are already using it. The latest forecast puts its chance of use in the next 30 days at over 99%. If you run an affected version, patch it first.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-41773

## At a glance

- **Verdict:** Fix this now. Attackers are using this flaw today. If you run an affected version, it goes to the top of your list.
- **Precursor Intelligence risk score:** 77 out of 100 (High); action: Emergency patch. Kept up to date as the evidence changes.
- **Severity:** High (CVSS 7.5 out of 10)
- **Known to be exploited:** Yes, it is on the government list of flaws known to be exploited
- **Chance of use in the next 30 days:** over 99% (latest exploit-likelihood forecast)
- **Published:** 5 October 2021
- **Record last updated:** 27 October 2025
- **Main product:** HTTP Server from Apache
- **Affected products:** 4

## What is CVE-2021-41773? In plain terms

It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data.

### The official description

A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions. The fix in Apache HTTP Server 2.4.50 was found to be incomplete, see CVE-2021-42013.

### 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: No login needed
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can read data

Severity vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`

## Is CVE-2021-41773 being exploited? Yes

Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%.

Exploit likelihood over the last 7 days: >99%, >99%, >99%, >99%, >99%, >99%, >99%.

### Timeline

- 5 October 2021: Published
- 27 October 2025: Record last updated

### How Precursor Intelligence ranks it

CVE-2021-41773 scores **77 out of 100 (High)**, with the action "Emergency patch".

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-2021-41773?

The published record lists 4 products.

- [HTTP Server](https://www.precursorintelligence.com/product/apache/http_server) by [Apache](https://www.precursorintelligence.com/vendors/apache) (Application): 2.4.49
- [Instantis Enterprisetrack](https://www.precursorintelligence.com/product/oracle/instantis_enterprisetrack) by [Oracle](https://www.precursorintelligence.com/vendors/oracle) (Application): 17.1, 17.2, 17.3
- [Fedora](https://www.precursorintelligence.com/product/fedoraproject/fedora) by [Fedoraproject](https://www.precursorintelligence.com/vendors/fedoraproject) (Operating system): 34, 35
- [Cloud Backup](https://www.precursorintelligence.com/product/netapp/cloud_backup) by [Netapp](https://www.precursorintelligence.com/vendors/netapp) (Application): version not specified

## How do I fix CVE-2021-41773?

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 advisories and patch notes 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. **Check it wasn’t used before you patched.** Because criminals are already using this flaw, look for signs of a break-in on affected systems using the vendor’s guidance.

### References

- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/11/4) (Mailing list, Patch, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/15/3) (Mailing list, Patch, Third-party advisory)
- [lists.apache.org](https://lists.apache.org/thread.html/r17a4c6ce9aff662efd9459e9d1850ab4a611cb23392fc68264c72cb3%40%3Ccvs.httpd.apache.org%3E) (Mailing list, Patch)
- [oracle.com](https://www.oracle.com/security-alerts/cpujan2022.html) (Patch, Third-party advisory)
- [httpd.apache.org](https://httpd.apache.org/security/vulnerabilities_24.html) (Release notes, Vendor advisory)
- [packetstormsecurity.com](http://packetstormsecurity.com/files/164418/Apache-HTTP-Server-2.4.49-Path-Traversal-Remote-Code-Execution.html) (Exploit, Third-party advisory, Vulnerability database)
- [packetstormsecurity.com](http://packetstormsecurity.com/files/164418/Apache-HTTP-Server-2.4.49-Path-Traversal.html) (Exploit, Third-party advisory, Vulnerability database)
- [packetstormsecurity.com](http://packetstormsecurity.com/files/164629/Apache-2.4.49-2.4.50-Traversal-Remote-Code-Execution.html) (Exploit, Third-party advisory, Vulnerability database)
- [packetstormsecurity.com](http://packetstormsecurity.com/files/164941/Apache-HTTP-Server-2.4.50-Remote-Code-Execution.html) (Exploit, Third-party advisory, Vulnerability database)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/05/2) (Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/07/1) (Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/07/6) (Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/08/1) (Exploit, Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/08/2) (Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/08/3) (Exploit, Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/08/4) (Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/08/5) (Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/08/6) (Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/09/1) (Mailing list, Third-party advisory)
- [openwall.com](http://www.openwall.com/lists/oss-security/2021/10/16/1) (Mailing list, Third-party advisory)
- [lists.apache.org](https://lists.apache.org/thread.html/r6abf5f2ba6f1aa8b1030f95367aaf17660c4e4c78cb2338aee18982f%40%3Cusers.httpd.apache.org%3E) (Mailing list)
- [lists.apache.org](https://lists.apache.org/thread.html/r7c795cd45a3384d4d27e57618a215b0ed19cb6ca8eb070061ad5d837%40%3Cannounce.apache.org%3E) (Mailing list)
- [lists.apache.org](https://lists.apache.org/thread.html/r98d704ed4377ed889d40479db79ed1ee2f43b2ebdd79ce84b042df45%40%3Cannounce.apache.org%3E) (Mailing list)
- [lists.apache.org](https://lists.apache.org/thread.html/rb5b0e46f179f60b0c70204656bc52fcb558e961cb4d06a971e9e3efb%40%3Cusers.httpd.apache.org%3E) (Mailing list)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RMIIEFINL6FUIOPD2A3M5XC6DH45Y3CC/) (Release notes)
- [lists.fedoraproject.org](https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WS5RVHOIIRECG65ZBTZY7IEJVWQSQPG3/) (Release notes)
- [security.gentoo.org](https://security.gentoo.org/glsa/202208-20) (Third-party advisory)
- [security.netapp.com](https://security.netapp.com/advisory/ntap-20211029-0009/) (Third-party advisory)
- [tools.cisco.com](https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-apache-httpd-pathtrv-LAzg68cZ) (Third-party advisory)

## Questions

### What is CVE-2021-41773?

CVE-2021-41773 is a high-severity flaw in HTTP Server from Apache, published on 5 October 2021. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data.

### How serious is CVE-2021-41773?

It scores 7.5 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-41773 is 77 out of 100, which is High. Its action is "Emergency patch". Attackers are using this flaw today. If you run an affected version, it goes to the top of your list.

### Is CVE-2021-41773 being exploited?

Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%.

### Which versions does CVE-2021-41773 affect?

For HTTP Server from Apache: 2.4.49. The record lists 4 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2021-41773?

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. Because criminals are already using it, also check affected systems for signs of a break-in.

## Does CVE-2021-41773 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.

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