How severe is CVE-2021-42090?

CVE-2021-42090 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-42090 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-42090?

CVE-2021-42090 affects Zammad. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-42090?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-42090 published?

CVE-2021-42090 was published on 2021-10-07 and last updated on 2026-06-17.

CVE-2021-42090

CVE-2021-42090 is a critical-severity vulnerability in Zammad with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-502.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 2% (81st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-502
Affected product: Zammad
Published: 2021-10-07
Last modified: 2026-06-17

Description

An issue was discovered in Zammad before 4.1.1. The Form functionality allows remote code execution because deserialization is mishandled.

Frequently asked questions

What is CVE-2021-42090?: An issue was discovered in Zammad before 4.1.1. The Form functionality allows remote code execution because deserialization is mishandled.
How severe is CVE-2021-42090?: CVE-2021-42090 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-42090 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-42090?: CVE-2021-42090 affects Zammad. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-42090?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-42090 published?: CVE-2021-42090 was published on 2021-10-07 and last updated on 2026-06-17.

References

https://zammad.com/en/advisories/zaa-2021-14

Affected products (1)

cpe:2.3:a:zammad:zammad:*:*:*:*:*:*:*:*

More vulnerabilities in Zammad

CVE-2022-48021 — Critical (CVSS 9.8): A vulnerability in Zammad v5.3.0 allows attackers to execute arbitrary code or escalate privileges via a crafted…
CVE-2022-35490 — Critical (CVSS 9.8): Zammad 5.2.0 is vulnerable to privilege escalation. Zammad has a prevention against brute-force attacks trying to guess…
CVE-2021-42094 — Critical (CVSS 9.8): An issue was discovered in Zammad before 4.1.1. Command Injection can occur via custom Packages.
CVE-2020-26030 — Critical (CVSS 9.8): An issue was discovered in Zammad before 3.4.1. There is an authentication bypass in the SSO endpoint via a crafted…
CVE-2017-6080 — Critical (CVSS 9.8): An issue was discovered in Zammad before 1.0.4, 1.1.x before 1.1.3, and 1.2.x before 1.2.1, caused by lack of a…
CVE-2017-5619 — Critical (CVSS 9.8): An issue was discovered in Zammad before 1.0.4, 1.1.x before 1.1.3, and 1.2.x before 1.2.1. Attackers can login with…

All CVEs affecting Zammad →

Other CWE-502 (Deserialization of Untrusted Data) vulnerabilities

CVE-2026-41104 — Critical (CVSS 10.0): Deserialization of untrusted data in Microsoft Planetary Computer Pro allows an unauthorized attacker to disclose…
CVE-2026-43633 — Critical (CVSS 10.0): HestiaCP versions 1.9.0 through 1.9.4 contain a deserialization vulnerability in the web terminal component caused by a…
CVE-2026-33819 — Critical (CVSS 10.0): Deserialization of untrusted data in Microsoft Bing allows an unauthorized attacker to execute code over a network.
CVE-2026-20131 — Critical (CVSS 10.0): A vulnerability in the web-based management interface of Cisco Secure Firewall Management Center (FMC) Software could…
CVE-2026-25632 — Critical (CVSS 10.0): EPyT-Flow is a Python package designed for the easy generation of hydraulic and water quality scenario data of water…
CVE-2025-14931 — Critical (CVSS 10.0): Hugging Face smolagents Remote Python Executor Deserialization of Untrusted Data Remote Code Execution Vulnerability.…

Browse all CWE-502 (Deserialization of Untrusted Data) vulnerabilities →