How severe is CVE-2021-41263?

CVE-2021-41263 has a CVSS 3.x base score of 8.3, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity low, and availability high.

Is CVE-2021-41263 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (45th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-41263?

CVE-2021-41263 affects Discourse Rails Multisite. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-41263?

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

When was CVE-2021-41263 published?

CVE-2021-41263 was published on 2021-11-15 and last updated on 2026-06-17.

CVE-2021-41263

CVE-2021-41263 is a high-severity vulnerability in Discourse Rails Multisite with a CVSS 3.x base score of 8.3. 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-327.

Key facts

Severity: High (CVSS 3.x base score 8.3)
CVSS v2: 6.0
EPSS exploit prediction: 1% (45th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-327
Affected product: Discourse Rails Multisite
Published: 2021-11-15
Last modified: 2026-06-17

Description

rails_multisite provides multi-db support for Rails applications. In affected versions this vulnerability impacts any Rails applications using `rails_multisite` alongside Rails' signed/encrypted cookies. Depending on how the application makes use of these cookies, it may be possible for an attacker to re-use cookies on different 'sites' within a multi-site Rails application. The issue has been patched in v4 of the `rails_multisite` gem. Note that this upgrade will invalidate all previous signed/encrypted cookies. The impact of this invalidation will vary based on the application architecture.

Frequently asked questions

What is CVE-2021-41263?: rails_multisite provides multi-db support for Rails applications. In affected versions this vulnerability impacts any Rails applications using `rails_multisite` alongside Rails' signed/encrypted cookies. Depending on how the application makes use of these cookies, it may be possible for an attacker to re-use cookies on different 'sites' within a multi-site Rails application. The issue has been patched in v4 of the `rails_multisite` gem. Note that this upgrade will invalidate all previous signed/encrypted cookies. The impact of this invalidation will vary based on the application architecture.
How severe is CVE-2021-41263?: CVE-2021-41263 has a CVSS 3.x base score of 8.3, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity low, and availability high.
Is CVE-2021-41263 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (45th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-41263?: CVE-2021-41263 affects Discourse Rails Multisite. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-41263?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-41263 published?: CVE-2021-41263 was published on 2021-11-15 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:discourse:rails_multisite:*:*:*:*:*:ruby:*:*

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