How severe is CVE-2023-39953?

CVE-2023-39953 has a CVSS 3.x base score of 4.8, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2023-39953 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (36th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-39953?

CVE-2023-39953 affects Nextcloud User Oidc. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2023-39953?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2023-39953 published?

CVE-2023-39953 was published on 2023-08-10 and last updated on 2026-06-17.

CVE-2023-39953

CVE-2023-39953 is a medium-severity vulnerability in Nextcloud User Oidc with a CVSS 3.x base score of 4.8. 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-303.

Key facts

Severity: Medium (CVSS 3.x base score 4.8)
EPSS exploit prediction: 0% (36th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-303
Affected product: Nextcloud User Oidc
Published: 2023-08-10
Last modified: 2026-06-17

Description

user_oidc provides the OIDC connect user backend for Nextcloud, an open-source cloud platform. Starting in version 1.0.0 and prior to version 1.3.3, missing verification of the issuer would have allowed an attacker to perform a man-in-the-middle attack returning corrupted or known token they also have access to. user_oidc 1.3.3 contains a patch. No known workarounds are available.

Frequently asked questions

What is CVE-2023-39953?: user_oidc provides the OIDC connect user backend for Nextcloud, an open-source cloud platform. Starting in version 1.0.0 and prior to version 1.3.3, missing verification of the issuer would have allowed an attacker to perform a man-in-the-middle attack returning corrupted or known token they also have access to. user_oidc 1.3.3 contains a patch. No known workarounds are available.
How severe is CVE-2023-39953?: CVE-2023-39953 has a CVSS 3.x base score of 4.8, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2023-39953 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (36th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-39953?: CVE-2023-39953 affects Nextcloud User Oidc. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2023-39953?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2023-39953 published?: CVE-2023-39953 was published on 2023-08-10 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:nextcloud:user_oidc:*:*:*:*:*:*:*:*

More vulnerabilities in Nextcloud User Oidc

CVE-2023-32074 — High (CVSS 8.0): user_oidc app is an OpenID Connect user backend for Nextcloud. Authentication can be broken/bypassed in user_oidc app.…
CVE-2024-37312 — Medium (CVSS 6.3): user_oidc app is an OpenID Connect user backend for Nextcloud. Missing access control on the ID4me endpoint allows an…
CVE-2024-37886 — Medium (CVSS 5.4): user_oidc app is an OpenID Connect user backend for Nextcloud. An attacker could potentially trick the app into…
CVE-2023-28848 — Medium (CVSS 4.8): user_oidc is the OIDC connect user backend for Nextcloud, an open source collaboration platform. A vulnerability in…
CVE-2026-45284 — Medium (CVSS 4.6): Nextcloud is an open source content collaboration platform. From version 1.3.6 to before version 8.4.0, an improper…
CVE-2023-39954 — Low (CVSS 3.8): user_oidc provides the OIDC connect user backend for Nextcloud, an open-source cloud platform. Starting in version…

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