PatchTheCVECVE-2021-22945: When sending data to an MQTT server, libcurl <= 7.73.0 and 7.78.0 could in some circumstances erroneously keep
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CRITICAL 9.1REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE
CVE-2021-22945 is a critical-severity flaw (CVSS 9.1) affecting libcurl, fedora, cloud backup. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
When sending data to an MQTT server, libcurl <= 7.73.0 and 7.78.0 could in some circumstances erroneously keep a pointer to an already freed memory area and both use that again in a subsequent call to send data and also free it *again*.
Why this priority
- Critical severity
- EPSS top 6%: 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 | 9.1 (Critical) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 6.7% (top 6%) |
| CISA exploited list | No |
| Weakness | CWE-415 |
| Published | 2021-09-23 |
| Last modified | 2026-10-14 |
Last updated 2026-10-14 · 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
haxx libcurl UPGRADE
Affected: >= 7.73.0 and <= 7.78.0
Fixed in: newer than 7.78.0
Safe to downgrade to: a release before 7.73.0
1. Check installed version
apt-cache policy libcurl || rpm -q libcurl || libcurl --version
2. UPGRADE to newer than 7.78.0 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade libcurl
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade libcurl
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 7.73.0 (Debian / Ubuntu)
apt-cache madison libcurl
sudo apt install libcurl=<VERSION_BEFORE_7.73.0>
sudo apt-mark hold libcurl
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list libcurl
sudo dnf downgrade libcurl-<VERSION_BEFORE_7.73.0>
sudo dnf versionlock add libcurl
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: 33 · 35
Fixed in: no fixed release known
Safe to downgrade to: a release before 33
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.
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.
netapp clustered data ontap 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 clustered-data-ontap || rpm -q clustered-data-ontap || clustered-data-ontap --version
No fixed or unaffected release known
Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.
oracle mysql server UPGRADE
Affected: >= 5.7.0 and <= 5.7.35 · >= 8.0.0 and <= 8.0.26
Fixed in: newer than 8.0.26
Safe to downgrade to: a release before 5.7.0
1. Check installed version
apt-cache policy mysql-server || rpm -q mysql-server || mysql-server --version
2. UPGRADE to newer than 8.0.26 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade mysql-server
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade mysql-server
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 5.7.0 (Debian / Ubuntu)
apt-cache madison mysql-server
sudo apt install mysql-server=<VERSION_BEFORE_5.7.0>
sudo apt-mark hold mysql-server
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list mysql-server
sudo dnf downgrade mysql-server-<VERSION_BEFORE_5.7.0>
sudo dnf versionlock add mysql-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.
netapp h300s firmware MITIGATE
Affected: all versions
Fixed in: no fixed release known
Safe to downgrade to: no unaffected older release
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.
Exact fixes by distribution
A distro patch exists: prefer upgrading over downgrading.
Fedora ELN · python-discovery · FIXED · 1.9.0-1.eln159 · FEDORA-2026-7a881c0c99 · source
sudo dnf upgrade --advisory=FEDORA-2026-7a881c0c99
Fedora 46 · pipx · FIXED · 1.18.11-1.fc46 · FEDORA-2026-443a765287 · source
sudo dnf upgrade --advisory=FEDORA-2026-443a765287
Ubuntu 22.04 · curl · FIXED · 7.74.0-1.3ubuntu2
sudo apt update && sudo apt install --only-upgrade curl
dpkg --compare-versions "$(dpkg-query -W -f='${Version}' curl)" ge "7.74.0-1.3ubuntu2" && echo PATCHED || echo STILL-VULNERABLE
Ubuntu 20.04 · curl · NOT AFFECTED
Debian 12 · curl · FIXED · 7.79.1-1
sudo apt update && sudo apt install --only-upgrade curl
dpkg --compare-versions "$(dpkg-query -W -f='${Version}' curl)" ge "7.79.1-1" && echo PATCHED || echo STILL-VULNERABLE
Debian 13 · curl · FIXED · 7.79.1-1
sudo apt update && sudo apt install --only-upgrade curl
dpkg --compare-versions "$(dpkg-query -W -f='${Version}' curl)" ge "7.79.1-1" && echo PATCHED || echo STILL-VULNERABLE
RHEL 6 · curl · NOT AFFECTED
RHEL 7 · curl · NOT AFFECTED
RHEL 8 · curl · NOT AFFECTED
RHEL 9 · curl · NOT AFFECTED
Alpine 3.20 · curl · FIXED · curl-7.79.0-r0
apk add --upgrade curl
apk info -v curl
Alpine 3.21 · curl · FIXED · curl-7.79.0-r0
apk add --upgrade curl
apk info -v curl
Alpine 3.22 · curl · FIXED · curl-7.79.0-r0
apk add --upgrade curl
apk info -v curl
Alpine 3.23 · curl · FIXED · curl-7.79.0-r0
apk add --upgrade curl
apk info -v curl
sudo yum update --advisory=ALAS2-2021-1724
Public exploits and detection
Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.
- Write-up: cert-portal.siemens.com/productcert/html/ssa-389290.html
- Write-up: www.oracle.com/security-alerts/cpuoct2021.html
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-2021-22945?
libcurl: upgrade to newer than 7.78.0; fedora: mitigate or apply the listed mitigation; cloud backup: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2021-22945 being exploited?
CVE-2021-22945 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-2021-22945 affect?
CVE-2021-22945 affects libcurl, fedora, cloud backup. Severity is critical (CVSS 9.1). When sending data to an MQTT server, libcurl <= 7.73.0 and 7.78.0 could in some circumstances erroneously keep a pointer to an already freed memory area and both use that again in a subsequent call to send data and also free it *again*.
How urgent is CVE-2021-22945?
Priority 70/100. Critical severity; EPSS top 6%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist
Software pages
MySQL vulnerabilities · curl vulnerabilities
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