How severe is CVE-2026-21806?

CVE-2026-21806 has a CVSS score of 3.1/10, rated LOW. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-21806?

Affected package information for CVE-2026-21806 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2026-21806?

No fixed release is recorded for CVE-2026-21806 yet. Track the upstream advisory, and apply the exposure-reduction steps below in the meantime.

How do I detect CVE-2026-21806 in my code and dependencies?

Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).

How do I mitigate CVE-2026-21806 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-21806 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-21806 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-21806?

CVE-2026-21806 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 4th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-21806?

CVE-2026-21806 is classified as CWE-557 (CWE-557). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-21806 published, and has it been updated?

CVE-2026-21806 was published on September 18, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🛡️

Not in CISA KEV

LOW severity

CVE-2026-21806

LOW

CVE-2026-21806 is a low-severity (CVSS 3.1) CWE-557 vulnerability. No vendor fix is recorded yet; mitigation options are listed below.

HCL BigFix Service Management is affected by an Administrative Session Concurrency vulnerability. The application allows multiple simultaneous authenticated sessions for the same administrative…

Published

Sep 18, 2026

Updated

Sep 18, 2026

Affected

1 product

Patched

See advisory

Exploits

None indexed

Exploitation data as of Oct 14, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-21806.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs4th percentile — riskier than 4% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-21806 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Description

HCL BigFix Service Management is affected by an Administrative Session Concurrency vulnerability. The application allows multiple simultaneous authenticated sessions for the same administrative account, which could enable an unauthorized attacker to predict or hijack valid session identifiers. Successful exploitation allows an attacker to compromise affected administrative sessions and execute actions with full privileged user permissions.

Affected Products

1 product · 1 configurations

Application

bigfix service managementhcltech

1 version

Detection & mitigation playbook

Vulnerability

Detect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).
Remediation status
No fixed release is recorded for CVE-2026-21806 yet. Track the upstream advisory, and apply the exposure-reduction steps below in the meantime.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

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