Security readout for executives and security teams
Plain-English summary
Concourse’s login flow could redirect users to an attacker-controlled site. If a user clicked a crafted OAuth login link, their Concourse access token could be exposed. This is a user-interaction issue, not an automatic server compromise, but token theft can affect CI/CD access.
Executive priority
Treat this as a high-priority CI/CD access risk where affected Concourse instances remain below 6.0.0. The main business concern is stolen user tokens leading to unauthorized pipeline access or disruption.
Technical view
CVE-2020-5409 is a CWE-601 open redirect in Pivotal Concourse’s /sky/login endpoint. Most versions before 6.0.0 allowed untrusted redirect destinations in OAuth login handling, potentially leaking a user’s Concourse access token after a click. CVSS v3.0 score is 7.6.
Likely exposure
Exposure is likely limited to Pivotal Concourse deployments running most versions before 6.0.0, especially environments where users authenticate through OAuth and can receive external links to the login flow.
Exploitation context
The provided sources do not show active exploitation, and KEV is false. Exploitation requires a remote unauthenticated attacker to convince a user to click a malicious OAuth redirect link, after which the user’s Concourse access token may be exposed.
Researcher notes
The issue is similar to, but distinct from, CVE-2018-15798. The source bundle names broad affected versions only, so exact affected build ranges and vendor-specific fix details should be confirmed against the Tanzu advisory.
Mitigation direction
- Inventory Concourse deployments and identify versions older than 6.0.0.
- Upgrade affected Concourse instances to 6.0.0 or later per vendor guidance.
- Review VMware Tanzu advisory for any environment-specific remediation notes.
- Consider rotating tokens for users suspected of clicking malicious login links.
Validation and detection
- Confirm every Concourse instance reports version 6.0.0 or later.
- Verify /sky/login no longer permits redirects to untrusted domains.
- Review authentication logs for suspicious redirects or unexpected token use.
- Check incident records for user reports of unusual Concourse login links.
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 lookupCredential and access behavior lookup
The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2020-5409 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
- High
- CVSS
- 7.6 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
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:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H2.84.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
7.6HighVector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://tanzu.vmware.com/security/cve-2020-5409CVE reference · x_refsource_CONFIRM
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.