Security readout for executives and security teams
Plain-English summary
Kanboard versions before 1.2.49 can be abused to send logged-in users from a trusted Kanboard link to an attacker-controlled site. The main business risk is phishing, credential theft, or malware delivery through user deception. This is not listed as known exploited in KEV, and the reported severity is medium.
Executive priority
Treat as a near-term hygiene fix, not an emergency based on current evidence. Upgrade affected Kanboard systems to reduce phishing risk that could lead to credential compromise or malware exposure. Prioritize externally accessible or business-critical instances.
Technical view
CVE-2026-21879 is a CWE-601 open redirect in Kanboard before 1.2.49. Protocol-relative URLs can bypass URL validation, allowing redirection of authenticated users to external attacker-controlled destinations. CVSS 3.1 is 4.7: network reachable, low complexity, no privileges required, user interaction required, changed scope, low confidentiality impact.
Likely exposure
Organizations running self-hosted Kanboard 1.2.48 or earlier are affected. Exposure is most relevant where Kanboard is reachable by users through browsers and trusted links are likely to be clicked. Systems already upgraded to 1.2.49 are reported fixed.
Exploitation context
Sources describe a phishing-oriented open redirect requiring user interaction. The issue can help attackers make malicious links appear tied to a trusted Kanboard domain. The provided sources do not state active exploitation, and the CVE is not marked KEV in the supplied data.
Researcher notes
The advisory attributes the weakness to URL validation bypass with protocol-relative URLs. The fix is linked in commit 93bcae03301a6d34185a8dba977417e6b3de519f and release v1.2.49. No public exploitation claim is present in the provided sources.
Mitigation direction
- Upgrade Kanboard to version 1.2.49 or later.
- Review the Kanboard GitHub advisory and release notes.
- Prioritize internet-accessible or widely used Kanboard instances.
- Warn users about unexpected Kanboard links until upgraded.
Validation and detection
- Inventory Kanboard deployments and record installed versions.
- Confirm affected instances are below version 1.2.49.
- Verify upgraded systems report version 1.2.49 or later.
- Review web logs for unusual redirect-related link activity.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-601: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-21879 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 4.7 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N2.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.7MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/kanboard/kanboard/security/advisories/GHSA-mhv9-7m9w-7hcqCVE reference · x_refsource_CONFIRM
- https://github.com/kanboard/kanboard/commit/93bcae03301a6d34185a8dba977417e6b3de519fCVE reference · x_refsource_MISC
- https://github.com/kanboard/kanboard/releases/tag/v1.2.49CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
URL Redirection to Untrusted Site ('Open Redirect')
URL Redirection to Untrusted Site ('Open Redirect') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.