PatchTheCVECVE-2016-9841: inffast.c in zlib 1.2.8 might allow context-dependent attackers to have unspecified impact by leveraging impro
68
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CRITICAL 9.8REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE
CVE-2016-9841 is a critical-severity flaw (CVSS 9.8) affecting zlib, leap, opensuse. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
inffast.c in zlib 1.2.8 might allow context-dependent attackers to have unspecified impact by leveraging improper pointer arithmetic.
Why this priority
- Critical severity
- EPSS top 5%: very likely to be exploited
- 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 | 7.5% (top 5%) |
| CISA exploited list | No |
| Published | 2017-05-23 |
| Last modified | 2026-10-08 |
Last updated 2026-10-08 · 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
zlib zlib UPGRADE
Affected: >= 1.2.0 and < 1.2.9
Fixed in: 1.2.9
Safe to downgrade to: a release before 1.2.0
1. Check installed version
apt-cache policy zlib || rpm -q zlib || zlib --version
2. UPGRADE to 1.2.9 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade zlib
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade zlib
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 1.2.0 (Debian / Ubuntu)
apt-cache madison zlib
sudo apt install zlib=<VERSION_BEFORE_1.2.0>
sudo apt-mark hold zlib
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list zlib
sudo dnf downgrade zlib-<VERSION_BEFORE_1.2.0>
sudo dnf versionlock add zlib
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.
opensuse leap MITIGATE
Affected: 42.1 · 42.2
Fixed in: no fixed release known
Safe to downgrade to: a release before 42.1
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.
opensuse opensuse MITIGATE
Affected: 13.2
Fixed in: no fixed release known
Safe to downgrade to: a release before 13.2
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: 8.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 8.0
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.
canonical ubuntu linux MITIGATE
Affected: 16.04 · 18.04
Fixed in: no fixed release known
Safe to downgrade to: a release before 16.04
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 database server DOWNGRADE
Affected: 18c
Fixed in: no fixed release known
Safe to downgrade to: a release before 18c
1. Check installed version
apt-cache policy database-server || rpm -q database-server || database-server --version
2. No fixed release: DOWNGRADE to a release before 18c (Debian / Ubuntu)
apt-cache madison database-server
sudo apt install database-server=<VERSION_BEFORE_18c>
sudo apt-mark hold database-server
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list database-server
sudo dnf downgrade database-server-<VERSION_BEFORE_18c>
sudo dnf versionlock add database-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.
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-2016-9841?
zlib: upgrade to 1.2.9; leap: mitigate or apply the listed mitigation; opensuse: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2016-9841 being exploited?
CVE-2016-9841 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-2016-9841 affect?
CVE-2016-9841 affects zlib, leap, opensuse. Severity is critical (CVSS 9.8). inffast.c in zlib 1.2.8 might allow context-dependent attackers to have unspecified impact by leveraging improper pointer arithmetic.
How urgent is CVE-2016-9841?
Priority 68/100. Critical severity; EPSS top 5%: very likely to be exploited; Remotely exploitable, no login, no user action; On your watchlist
Software pages
Oracle Database vulnerabilities · Ubuntu vulnerabilities · Debian vulnerabilities · zlib vulnerabilities
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