Security readout for executives and security teams
Plain-English summary
TerriaJS-Server versions before 4.0.3 can be tricked into proxying requests to domains that were not approved in its allowlist. For organizations using TerriaJS geospatial portals, this weakens a key boundary intended to control where the server can send traffic. The vendor-fixed version is 4.0.3.
Executive priority
Prioritize remediation for public-facing TerriaJS deployments or portals handling sensitive workflows. The issue is high severity because unauthenticated remote users may bypass proxy destination controls. Upgrade to 4.0.3 should be treated as the primary action.
Technical view
CVE-2026-27818 is an input validation flaw in TerriaJS-Server’s proxy allowlist handling. The CVE maps to CWE-20 and CWE-918. It is network-reachable, requires no authentication or user interaction, and has CVSS 4.0 score 8.7. Affected versions are terriajs-server earlier than 4.0.3.
Likely exposure
Exposure is likely where TerriaJS-Server versions below 4.0.3 are deployed and the proxy feature is reachable by untrusted users or the internet. Risk depends on how proxyableDomains is configured and what internal or external destinations the server can reach.
Exploitation context
Sources state attackers can bypass configured proxyableDomains restrictions and proxy domains not explicitly allowed. The bundle does not show CISA KEV listing or other evidence of active exploitation. No public exploit status is established from the provided sources.
Researcher notes
The supplied advisory identifies a domain validation bypass in proxy allowlist enforcement. The commit reference is the vendor fix, but deeper code-level analysis should rely on that diff and advisory. Avoid assuming broader SSRF impact beyond the stated ability to proxy unallowed domains.
Mitigation direction
- Upgrade terriajs-server to version 4.0.3 or later.
- Review the GitHub security advisory for vendor-specific guidance.
- Restrict exposure to proxy functionality until the upgrade is complete.
- Review proxyableDomains for intended, minimal allowed destinations.
Validation and detection
- Inventory applications using TerriaJS-Server.
- Confirm installed terriajs-server versions are 4.0.3 or later.
- Review proxy logs for unexpected destination domains.
- Verify proxyableDomains contains only approved domains.
- Check whether the proxy endpoint is internet-accessible.
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-20: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. 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 lookupCWE-918: Information exposure and cloud metadata lookup
Information exposure and SSRF weaknesses can make discovery, cloud metadata, and credential material review relevant. 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-2026-27818 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
- 8.7 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA: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:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N——Primary CVE scoreVulnerability scoring details
Base CVSS 4.0 score
8.7HighVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/TerriaJS/terriajs-server/security/advisories/GHSA-w789-49fc-v8hrCVE reference · x_refsource_CONFIRM
- https://github.com/TerriaJS/terriajs-server/commit/3aaa5d9717162b245ae4569232bbe7d8673c913fCVE 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.
Improper Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Server-Side Request Forgery (SSRF)
Server-Side Request Forgery (SSRF) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.