PatchTheCVECVE-2021-44790: A carefully crafted request body can cause a buffer overflow in the mod_lua multipart parser (r:parsebody() ca
74
This week
CRITICAL 9.8REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE
CVE-2021-44790 is a critical-severity flaw (CVSS 9.8) affecting http server, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
A carefully crafted request body can cause a buffer overflow in the mod_lua multipart parser (r:parsebody() called from Lua scripts). The Apache httpd team is not aware of an exploit for the vulnerabilty though it might be possible to craft one. This issue affects Apache HTTP Server 2.4.51 and earlier.
Why this priority
- Critical severity
- EPSS top 1%: very likely to be exploited
- Public exploit reference
- Remotely exploitable, no login, no user action
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 9.8 (Critical) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 96.8% (top 1%) |
| CISA exploited list | No |
| Weakness | CWE-787 |
| Published | 2021-12-20 |
| Last modified | 2026-06-17 |
Publisher (CNA): Apache Software Foundation · Vendor: apache · debian · fedoraproject · netapp · oracle · tenable
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
apache http server UPGRADE
Affected: < 2.4.52
Fixed in: 2.4.52
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy http-server || rpm -q http-server || http-server --version
2. UPGRADE to 2.4.52 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade http-server
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade http-server
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
fedoraproject fedora MITIGATE
Affected: 34 · 35 · 36
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.
debian debian linux MITIGATE
Affected: 10.0 · 11.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 10.0
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.
tenable tenable.sc UPGRADE
Affected: >= 5.16.0 and < 5.20.0
Fixed in: 5.20.0
Safe to downgrade to: a release before 5.16.0
1. Check installed version
apt-cache policy tenable.sc || rpm -q tenable.sc || tenable.sc --version
2. UPGRADE to 5.20.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade tenable.sc
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade tenable.sc
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 5.16.0 (Debian / Ubuntu)
apt-cache madison tenable.sc
sudo apt install tenable.sc=<VERSION_BEFORE_5.16.0>
sudo apt-mark hold tenable.sc
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list tenable.sc
sudo dnf downgrade tenable.sc-<VERSION_BEFORE_5.16.0>
sudo dnf versionlock add tenable.sc
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.
oracle communications element manager UPGRADE
Affected: <= 9.0
Fixed in: newer than 9.0
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy communications-element-manager || rpm -q communications-element-manager || communications-element-manager --version
2. UPGRADE to newer than 9.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade communications-element-manager
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade communications-element-manager
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
Exact fixes by distribution
A distro patch exists: prefer upgrading over downgrading.
Fedora 46 · nemo · FIXED · 6.8.0-1.fc46 · FEDORA-2026-0edead723f · source
sudo dnf upgrade --advisory=FEDORA-2026-0edead723f
Fedora ELN · composer · FIXED · 2.11.1-1.eln159 · FEDORA-2026-cb4f992456 · source
sudo dnf upgrade --advisory=FEDORA-2026-cb4f992456
Ubuntu 20.04 · apache2 · FIXED · 2.4.41-4ubuntu3.9
sudo apt update && sudo apt install --only-upgrade apache2
dpkg --compare-versions "$(dpkg-query -W -f='${Version}' apache2)" ge "2.4.41-4ubuntu3.9" && echo PATCHED || echo STILL-VULNERABLE
Ubuntu 22.04 · apache2 · FIXED · 2.4.52-1ubuntu1
sudo apt update && sudo apt install --only-upgrade apache2
dpkg --compare-versions "$(dpkg-query -W -f='${Version}' apache2)" ge "2.4.52-1ubuntu1" && echo PATCHED || echo STILL-VULNERABLE
Debian 12 · apache2 · FIXED · 2.4.52-1
sudo apt update && sudo apt install --only-upgrade apache2
dpkg --compare-versions "$(dpkg-query -W -f='${Version}' apache2)" ge "2.4.52-1" && echo PATCHED || echo STILL-VULNERABLE
Debian 13 · apache2 · FIXED · 2.4.52-1
sudo apt update && sudo apt install --only-upgrade apache2
dpkg --compare-versions "$(dpkg-query -W -f='${Version}' apache2)" ge "2.4.52-1" && echo PATCHED || echo STILL-VULNERABLE
RHEL 7 · httpd · FIXED · httpd-2.4.6-97.el7_9.4
sudo dnf upgrade --advisory=RHSA-2022:0143
rpm -q httpd
RHEL 7.3 Advanced Update Support · httpd · FIXED · httpd-2.4.6-45.el7_3.8
sudo dnf upgrade --advisory=RHSA-2022:1139
rpm -q httpd
RHEL 7.4 Advanced Update Support · httpd · FIXED · httpd-2.4.6-67.el7_4.9
sudo dnf upgrade --advisory=RHSA-2022:1138
rpm -q httpd
RHEL 7.6 Advanced Update Support · httpd · FIXED · httpd-2.4.6-89.el7_6.4
sudo dnf upgrade --advisory=RHSA-2022:1136
rpm -q httpd
RHEL 7.6 Telco Extended Update Support · httpd · FIXED · httpd-2.4.6-89.el7_6.4
sudo dnf upgrade --advisory=RHSA-2022:1136
rpm -q httpd
Alpine 3.20 · apache2 · FIXED · apache2-2.4.52-r0
apk add --upgrade apache2
apk info -v apache2
Alpine 3.21 · apache2 · FIXED · apache2-2.4.52-r0
apk add --upgrade apache2
apk info -v apache2
Alpine 3.22 · apache2 · FIXED · apache2-2.4.52-r0
apk add --upgrade apache2
apk info -v apache2
Alpine 3.23 · apache2 · FIXED · apache2-2.4.52-r0
apk add --upgrade apache2
apk info -v apache2
sudo dnf update --advisory=ALAS2023-2023-072
sudo yum update --advisory=ALAS2-2022-1737
sudo yum update --advisory=ALAS-2022-1560
Public exploits and detection
Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.
- GitHub PoC: nuPacaChi/-CVE-2021-44790 (4 stars)
- GitHub PoC: CerberusMrXi/Apache-Lua-Buffer-Overflow-Exploit-CVE-2021-44790 (1 stars)
- GitHub PoC: MohammadAliMehri/cve-2021-44790-lab (0 stars)
- Write-up: www.oracle.com/security-alerts/cpuapr2022.html
- Write-up: www.oracle.com/security-alerts/cpujan2022.html
- Exploit-DB: Apache 2.4.x - Buffer Overflow
Verify at the official source NVD · CVE Program · 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.
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-2021-44790?
http server: upgrade to 2.4.52; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2021-44790 being exploited?
CVE-2021-44790 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2021-44790 affect?
CVE-2021-44790 affects http server, fedora, debian linux. Severity is critical (CVSS 9.8). A carefully crafted request body can cause a buffer overflow in the mod_lua multipart parser (r:parsebody() called from Lua scripts). The Apache httpd team is not aware of an exploit for the vulnerabilty though it might be possible to craft
How urgent is CVE-2021-44790?
Priority 74/100. Critical severity; EPSS top 1%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist
Software pages
Apache HTTP Server vulnerabilities · Debian vulnerabilities
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