How severe is CVE-2026-27818?

No CVSS score has been assigned to CVE-2026-27818 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-27818?

CVE-2026-27818 affects the following packages: terriajs-server (npm). Ecosystems affected: npm.

How do I fix CVE-2026-27818?

Update terriajs-server to 4.0.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27818 is resolved across your whole dependency graph.

How do I detect CVE-2026-27818 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for terriajs-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-27818 if there is no patch (or I can't update yet)?

Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.

Is CVE-2026-27818 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-27818 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-27818?

CVE-2026-27818 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 21th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-27818?

CVE-2026-27818 is classified as Improper Input Validation (CWE-20), Server-Side Request Forgery (SSRF) (CWE-918). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-27818 published, and has it been updated?

CVE-2026-27818 was published on February 26, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2026-27818 — terriajs-server

Fix: TerriaJS/terriajs-server@3aaa5d9

CVE-2026-27818 is a Improper Input Validation vulnerability in terriajs-server. A fix is available for terriajs-server — see the affected versions and patch details below.

TerriaJS-Server has a domain validation bypass vulnerability in its proxy allowlist

Also known asGHSA-w789-49fc-v8hr

Published

Feb 26, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 30, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27818.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk-0.13%

Lower risk than most CVEs21th percentile — riskier than 21% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

2other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

terriajs-servernpm

2Kdownloads / week

Description

Impact

A validation bug allows an attacker to proxy domains not explicitly allowed in the proxyableDomains configuration.

The validation only checks if a hostname ended with an allowed domain. This meant:

If example.com is allowed in proxyableDomains:

✅ example.com is allowed (correct)
✅ api.example.com is allowed (correct)
⚠️ maliciousexample.com is allowed (incorrect)

An attacker could register maliciousexample.com and proxy content through terriajs-server, bypassing proxy restrictions.

Patches

All versions up to 4.0.2 are affected. Upgrade to 4.0.3 to address the vulnerability.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`terriajs-server`	all versions	4.0.3`npm install terriajs-server@4.0.3`

Affected Products

1 product · 1 configurations

Application

terriajs-serverterria

< 4.0.3

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for terriajs-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update terriajs-server to 4.0.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27818 is resolved across your whole dependency graph.
Workarounds
Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.

Frequently Asked Questions

### Impact A validation bug allows an attacker to proxy domains not explicitly allowed in the `proxyableDomains` configuration. The validation only checks if a hostname _ended_ with an allowed domain. This meant: If `example.com` is allowed in `proxyableDomains`: - ✅ example.com is allowed (correct) - ✅ api.example.com is allowed (correct) - ⚠️ maliciousexample.com is allowed (incorrect) An attacker could register maliciousexample.com and proxy content through `terriajs-server`, bypassing proxy restrictions. ### Patches All versions up to 4.0.2 are affected. Upgrade to 4.0.3 to address th

O3 Security · Impact-Aware SCA

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