CVE-1999-0433: XFree86 startx command is vulnerable to a symlink attack, allowing local users to create files in restricted d

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MEDIUM 4.6WATCHLISTDOWNGRADEMITIGATEMITIGATE

CVE-1999-0433 is a medium-severity flaw (CVSS 4.6) affecting x11r6, netbsd, linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

XFree86 startx command is vulnerable to a symlink attack, allowing local users to create files in restricted directories, possibly allowing them to gain privileges or cause a denial of service.

Why this priority

Public exploit reference
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	4.6 (Medium)
EPSS exploit chance	0.7% (top 46%)
CISA exploited list	No
Published	1999-03-21
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: netbsd · redhat · slackware · suse · xfree86 project

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

1999-03-21 05:00 UTCPublished CVE record published
2026-06-16 21:48 UTCUpdated Record last modified

xfree86 project x11r6 DOWNGRADE

Affected: 3.3.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.3.3

1. Check installed version

apt-cache policy x11r6 || rpm -q x11r6 || x11r6 --version

2. No fixed release: DOWNGRADE to a release before 3.3.3 (Debian / Ubuntu)

apt-cache madison x11r6 sudo apt install x11r6=<VERSION_BEFORE_3.3.3> sudo apt-mark hold x11r6

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list x11r6 sudo dnf downgrade x11r6-<VERSION_BEFORE_3.3.3> sudo dnf versionlock add x11r6

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.

netbsd netbsd MITIGATE

Affected: 1.3.2 · 1.3.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.3.2

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.

redhat linux MITIGATE

Affected: 5.1 · 5.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.1

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.

slackware slackware linux MITIGATE

Affected: 3.3 · 3.4 · 3.5 · 3.6 · 4.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.3

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.

suse suse linux MITIGATE

Affected: 5.1 · 5.2 · 6.0 · 6.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.1

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.

Public exploits and detection

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

Exploit-DB: X11R6 3.3.3 - Symlink

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.

Quick answers

How do I fix CVE-1999-0433?

x11r6: downgrade or apply the listed mitigation; netbsd: mitigate or apply the listed mitigation; linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-1999-0433 being exploited?

CVE-1999-0433 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-1999-0433 affect?

CVE-1999-0433 affects x11r6, netbsd, linux. Severity is medium (CVSS 4.6). XFree86 startx command is vulnerable to a symlink attack, allowing local users to create files in restricted directories, possibly allowing them to gain privileges or cause a denial of service.

How urgent is CVE-1999-0433?

Priority 40/100. Public exploit reference; On your watchlist

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References

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