CVE-2021-45891: An issue was discovered in Softwarebuero Zauner ARC 4.2.0.4., that allows attackers to escalate privileges wit

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HIGH 8.8DOWNGRADE

CVE-2021-45891 is a high-severity flaw (CVSS 8.8) affecting arc. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in Softwarebuero Zauner ARC 4.2.0.4., that allows attackers to escalate privileges within the application, since all permission checks are done client-side, not server-side.

Why this priority

High severity
Public exploit reference

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

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.4% (top 27%)
CISA exploited list	No
Weakness	CWE-669
Published	2022-04-05
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: zauner

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

Am I affected?

Timeline

2022-04-05 02:15 UTCPublished CVE record published
2026-06-17 04:14 UTCUpdated Record last modified

zauner arc DOWNGRADE

Affected: 4.2.0.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.2.0.4

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 4.2.0.4 (Debian / Ubuntu)

apt-cache madison arc sudo apt install arc=<VERSION_BEFORE_4.2.0.4> sudo apt-mark hold arc

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

dnf --showduplicates list arc sudo dnf downgrade arc-<VERSION_BEFORE_4.2.0.4> sudo dnf versionlock add arc

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.

Quick answers

How do I fix CVE-2021-45891?

arc: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-45891 being exploited?

CVE-2021-45891 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-2021-45891 affect?

CVE-2021-45891 affects arc. Severity is high (CVSS 8.8). An issue was discovered in Softwarebuero Zauner ARC 4.2.0.4., that allows attackers to escalate privileges within the application, since all permission checks are done client-side, not server-side.

How urgent is CVE-2021-45891?

Priority 54/100. High severity; Public exploit reference

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CVE-2023-24243 HIGH 7.5 UPGRADE CData RSB Connect v22.0.8336 was discovered to contain a Server-Side Request Forgery (SSRF).
CVE-2021-45894 MEDIUM 5.9 DOWNGRADE An issue was discovered in Softwarebuero Zauner ARC 4.2.0.4
CVE-2021-45893 HIGH 7.5 DOWNGRADE An issue was discovered in Softwarebuero Zauner ARC 4.2.0.4

References

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