Free and open · new CVEs checked every 20 minutesStatusRSSOpen dataContact

CVE-2021-41773: Apache HTTP Server Path Traversal Vulnerability

100
Patch now
CRITICAL 9.8EXPLOITEDREMOTEWATCHLISTDOWNGRADEMITIGATEDOWNGRADE

CVE-2021-41773 is a critical-severity flaw (CVSS 9.8) affecting http server, fedora, instantis enterprisetrack, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 exec

Why this priority

  • Critical severity
  • EPSS top 1%: very likely to be exploited
  • Exploited in the wild (CISA KEV)
  • Used in ransomware campaigns
  • Public exploit reference
  • CISA SSVC: automatable with total technical impact
  • Remotely exploitable, no login, no user action
  • On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score9.8 (Critical)
Attack vectorNetwork (remote)
Attack complexityLow
Privileges neededNone
User interactionNone
EPSS exploit chance100.0% (top 1%)
CISA exploited listYes, fix due 2021-11-17, used in ransomware
WeaknessCWE-22
Published2021-10-05
Last modified2026-06-17
Publisher (CNA): Apache Software Foundation · Vendor: apache · fedoraproject · netapp · oracle

Share: LinkedIn · X · Reddit

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

apache http server DOWNGRADE
Affected: 2.4.49
Fixed in: no fixed release known
Safe to downgrade to: a release before 2.4.49
1. Check installed version
apt-cache policy http-server || rpm -q http-server || http-server --version
2. No fixed release: DOWNGRADE to a release before 2.4.49 (Debian / Ubuntu)
apt-cache madison http-server sudo apt install http-server=<VERSION_BEFORE_2.4.49> sudo apt-mark hold http-server
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list http-server sudo dnf downgrade http-server-<VERSION_BEFORE_2.4.49> sudo dnf versionlock add http-server
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
fedoraproject fedora MITIGATE
Affected: 34 · 35
Fixed in: no fixed release known
Safe to downgrade to: a release before 34
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
oracle instantis enterprisetrack DOWNGRADE
Affected: 17.1 · 17.2 · 17.3
Fixed in: no fixed release known
Safe to downgrade to: a release before 17.1
1. Check installed version
apt-cache policy instantis-enterprisetrack || rpm -q instantis-enterprisetrack || instantis-enterprisetrack --version
2. No fixed release: DOWNGRADE to a release before 17.1 (Debian / Ubuntu)
apt-cache madison instantis-enterprisetrack sudo apt install instantis-enterprisetrack=<VERSION_BEFORE_17.1> sudo apt-mark hold instantis-enterprisetrack
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list instantis-enterprisetrack sudo dnf downgrade instantis-enterprisetrack-<VERSION_BEFORE_17.1> sudo dnf versionlock add instantis-enterprisetrack
Downgrade risk
Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.
After downgrade
Restart the service, and keep the package held until a fixed release ships.
netapp cloud backup MITIGATE
Affected: all versions
Fixed in: no fixed release known
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy cloud-backup || rpm -q cloud-backup || cloud-backup --version
No fixed or unaffected release known
Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.
Fedora 46 · bitcoin-core-selinux · FIXED · 0.3-2.fc46 · FEDORA-2026-51fc806272 · source
sudo dnf upgrade --advisory=FEDORA-2026-51fc806272
Fedora ELN · guestfs-tools · FIXED · 1.57.5-1.eln159 · FEDORA-2026-9577c5ec16 · source
sudo dnf upgrade --advisory=FEDORA-2026-9577c5ec16
Ubuntu 22.04 · apache2 · NOT AFFECTED
Ubuntu 20.04 · apache2 · NOT AFFECTED
Debian 12 · apache2 · FIXED · 2.4.50-1
sudo apt update && sudo apt install --only-upgrade apache2 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' apache2)" ge "2.4.50-1" && echo PATCHED || echo STILL-VULNERABLE
Debian 13 · apache2 · FIXED · 2.4.50-1
sudo apt update && sudo apt install --only-upgrade apache2 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' apache2)" ge "2.4.50-1" && echo PATCHED || echo STILL-VULNERABLE
RHEL 6 · httpd · NOT AFFECTED
RHEL 7 · httpd · NOT AFFECTED
RHEL 8 · httpd:2.4/httpd · NOT AFFECTED
RHEL 9 · httpd · NOT AFFECTED
Alpine 3.20 · apache2 · FIXED · apache2-2.4.50-r0
apk add --upgrade apache2 apk info -v apache2
Alpine 3.21 · apache2 · FIXED · apache2-2.4.50-r0
apk add --upgrade apache2 apk info -v apache2
Alpine 3.22 · apache2 · FIXED · apache2-2.4.50-r0
apk add --upgrade apache2 apk info -v apache2
Alpine 3.23 · apache2 · FIXED · apache2-2.4.50-r0
apk add --upgrade apache2 apk info -v apache2
Amazon Linux 2 · see advisory · FIXED · ALAS2-2021-1716 · source
sudo yum update --advisory=ALAS2-2021-1716
Amazon Linux 1 · see advisory · FIXED · ALAS-2021-1543 · source
sudo yum update --advisory=ALAS-2021-1543

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Advisories and coverage

Research and news

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-41773?

http server: downgrade or apply the listed mitigation; fedora: mitigate or apply the listed mitigation; instantis enterprisetrack: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-41773 being exploited?

Yes. CVE-2021-41773 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2021-41773 affect?

CVE-2021-41773 affects http server, fedora, instantis enterprisetrack. Severity is critical (CVSS 9.8). 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

How urgent is CVE-2021-41773?

Priority 100/100. Critical severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Used in ransomware campaigns; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Apache HTTP Server vulnerabilities

Related CVEs

References

← Back to latest CVEs

Get the weekly exploited-CVE digest by emailThe CVEs being attacked this week and how to fix them. No spam, unsubscribe any time.