CVE-2021-34992: This vulnerability allows remote attackers to execute arbitrary code on affected installations of Orckestra C1

This month

HIGH 8.8DOWNGRADE

CVE-2021-34992 is a high-severity flaw (CVSS 8.8) affecting c1 cms. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

This vulnerability allows remote attackers to execute arbitrary code on affected installations of Orckestra C1 CMS 6.10. Authentication is required to exploit this vulnerability. The specific flaw exists within Composite.dll. The issue results from the lack of proper validation of user-supplied data, which can result in deserialization of untrusted data. An attacker can leverage this vulnerability to execute code in the context of the service acc

Why this priority

High severity
EPSS top 9%: very likely to be exploited

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	4.3% (top 9%)
CISA exploited list	No
Weakness	CWE-502
Published	2021-11-15
Last modified	2026-06-17

Publisher (CNA): Zero Day Initiative · Vendor: orckestra

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

Am I affected?

Timeline

2021-11-15 16:15 UTCPublished CVE record published
2026-06-17 03:56 UTCUpdated Record last modified

orckestra c1 cms DOWNGRADE

Affected: 6.10

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.10

1. Check installed version

apt-cache policy c1-cms || rpm -q c1-cms || c1-cms --version

2. No fixed release: DOWNGRADE to a release before 6.10 (Debian / Ubuntu)

apt-cache madison c1-cms sudo apt install c1-cms=<VERSION_BEFORE_6.10> sudo apt-mark hold c1-cms

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

dnf --showduplicates list c1-cms sudo dnf downgrade c1-cms-<VERSION_BEFORE_6.10> sudo dnf versionlock add c1-cms

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-2021-34992?

c1 cms: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-34992 being exploited?

CVE-2021-34992 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-2021-34992 affect?

CVE-2021-34992 affects c1 cms. Severity is high (CVSS 8.8). This vulnerability allows remote attackers to execute arbitrary code on affected installations of Orckestra C1 CMS 6.10. Authentication is required to exploit this vulnerability. The specific flaw exists within Composite.dll. The issue resu

How urgent is CVE-2021-34992?

Priority 54/100. High severity; EPSS top 9%: very likely to be exploited

Related CVEs

CVE-2022-39256 CRITICAL 9.0 UPGRADE Orckestra C1 CMS is a .NET based Web Content Management System
CVE-2022-24789 HIGH 7.6 UPGRADE C1 CMS is an open-source, .NET based Content Management System (CMS)

References

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