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CVE-2020-26251

CORS configuration is possibly vulnerable

4.7 Medium

Open Zaak is a modern, open-source data- and services-layer to enable zaakgericht werken, a Dutch approach to case management. In Open Zaak before version 1.3.3 the Cross-Origin-Resource-Sharing policy in Open Zaak is currently wide open - every client is allowed. This allows evil.com to run scripts that perform AJAX calls to known Open Zaak installations, and the browser will not block these. This was intended to only apply to development machines running on localhost/127.0.0.1. Open Zaak 1.3.3 disables CORS by default, while it can be opted-in through environment variables. The vulnerability does not actually seem exploitable because: a) The session cookie has a Same-Site: Lax policy which prevents it from being sent along in Cross-Origin requests. b) All pages that give access to (production) data are login-protected c) Access-Control-Allow-Credentials is set to false d) CSRF checks probably block the remote origin, since they're not explicitly added to the trusted allowlist.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
None
User interaction
Required

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
None

Exploit likelihood

0.45%Down 0.4 points since Apr 14, 2021
90%50%10%1%

What each source reports

CVE List Score used 4.7

CORS configuration is possibly vulnerable

Open Zaak is a modern, open-source data- and services-layer to enable zaakgericht werken, a Dutch approach to case management. In Open Zaak before version 1.3.3 the Cross-Origin-Resource-Sharing policy in Open Zaak is currently wide open - every client is allowed. This allows evil.com to run scripts that perform AJAX calls to known Open Zaak installations, and the browser will not block these. This was intended to only apply to development machines running on localhost/127.0.0.1. Open Zaak 1.3.3 disables CORS by default, while it can be opted-in through environment variables. The vulnerability does not actually seem exploitable because: a) The session cookie has a Same-Site: Lax policy which prevents it from being sent along in Cross-Origin requests. b) All pages that give access to (production) data are login-protected c) Access-Control-Allow-Credentials is set to false d) CSRF checks probably block the remote origin, since they're not explicitly added to the trusted allowlist.

Record
CVE-2020-26251
CVSS 3.1
4.7 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-346
Updated
2026-11-02
EUVDEUVD-2020-18847 4.7

Open Zaak is a modern, open-source data- and services-layer to enable zaakgericht werken, a Dutch approach to case management. In Open Zaak before version 1.3.3 the Cross-Origin-Resource-Sharing policy in Open Zaak is currently wide open - every client is allowed. This allows evil.com to run scripts that perform AJAX calls to known Open Zaak installations, and the browser will not block these. This was intended to only apply to development machines running on localhost/127.0.0.1. Open Zaak 1.3.3 disables CORS by default, while it can be opted-in through environment variables. The vulnerability does not actually seem exploitable because: a) The session cookie has a Same-Site: Lax policy which prevents it from being sent along in Cross-Origin requests. b) All pages that give access to (production) data are login-protected c) Access-Control-Allow-Credentials is set to false d) CSRF checks probably block the remote origin, since they're not explicitly added to the trusted allowlist.

Record
EUVD-2020-18847
CVSS 3.1
4.7 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-03
NVD 4.7

Open Zaak is a modern, open-source data- and services-layer to enable zaakgericht werken, a Dutch approach to case management. In Open Zaak before version 1.3.3 the Cross-Origin-Resource-Sharing policy in Open Zaak is currently wide open - every client is allowed. This allows evil.com to run scripts that perform AJAX calls to known Open Zaak installations, and the browser will not block these. This was intended to only apply to development machines running on localhost/127.0.0.1. Open Zaak 1.3.3 disables CORS by default, while it can be opted-in through environment variables. The vulnerability does not actually seem exploitable because: a) The session cookie has a Same-Site: Lax policy which prevents it from being sent along in Cross-Origin requests. b) All pages that give access to (production) data are login-protected c) Access-Control-Allow-Credentials is set to false d) CSRF checks probably block the remote origin, since they're not explicitly added to the trusted allowlist.

Record
CVE-2020-26251
CVSS 3.1
4.7 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
CVSS 2.0
4.3 MediumAV:N/AC:M/Au:N/C:N/I:P/A:N
Weakness
CWE-346
Updated
2026-11-02
OSV 4.7

Open Zaak is a modern, open-source data- and services-layer to enable zaakgericht werken, a Dutch approach to case management. In Open Zaak before version 1.3.3 the Cross-Origin-Resource-Sharing policy in Open Zaak is currently wide open - every client is allowed. This allows evil.com to run scripts that perform AJAX calls to known Open Zaak installations, and the browser will not block these. This was intended to only apply to development machines running on localhost/127.0.0.1. Open Zaak 1.3.3 disables CORS by default, while it can be opted-in through environment variables. The vulnerability does not actually seem exploitable because: a) The session cookie has a Same-Site: Lax policy which prevents it from being sent along in Cross-Origin requests. b) All pages that give access to (production) data are login-protected c) Access-Control-Allow-Credentials is set to false d) CSRF checks probably block the remote origin, since they're not explicitly added to the trusted allowlist.

Record
CVE-2020-26251
CVSS 3.1
4.7 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02

Affected products

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2020-26251 is a medium vulnerability (CVSS 4.7) in Openzaak Open Zaak, published December 18, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.45%, the 39th percentile. No source names a fixed version.

References

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