How severe is CVE-2021-3311?

CVE-2021-3311 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-2021-3311 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3311?

CVE-2021-3311 affects Octobercms October. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-3311?

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-2021-3311 published?

CVE-2021-3311 was published on 2021-02-05 and last updated on 2026-06-17.

CVE-2021-3311

CVE-2021-3311 is a critical-severity vulnerability in Octobercms October 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-613.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 6.8
EPSS exploit prediction: 3% (85th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-613
Affected product: Octobercms October
Published: 2021-02-05
Last modified: 2026-06-17

Description

An issue was discovered in October through build 471. It reactivates an old session ID (which had been invalid after a logout) once a new login occurs. NOTE: this violates the intended Auth/Manager.php authentication behavior but, admittedly, is only relevant if an old session ID is known to an attacker.

Frequently asked questions

What is CVE-2021-3311?: An issue was discovered in October through build 471. It reactivates an old session ID (which had been invalid after a logout) once a new login occurs. NOTE: this violates the intended Auth/Manager.php authentication behavior but, admittedly, is only relevant if an old session ID is known to an attacker.
How severe is CVE-2021-3311?: CVE-2021-3311 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-2021-3311 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3311?: CVE-2021-3311 affects Octobercms October. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-3311?: 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-2021-3311 published?: CVE-2021-3311 was published on 2021-02-05 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:octobercms:october:*:*:*:*:*:*:*:*

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