GHSA-wrq8-fcv5-8hvp CVE-2026-55428 GO-2026-5915
Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator
- Severity
- 8.2 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.40%
- Chance of exploitation in the next 30 days. Higher than 34.75% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Fix
2.34.2- Upgrade github.com/coder/coder/v2 to this version or later
Description
Summary
The tailnet coordinator validates that an agent's Addresses derive from its authenticated UUID but applies no equivalent check to AllowedIPs. The coordinator forwards agent-supplied AllowedIPs verbatim to tunnel peers which install them into the WireGuard peer configuration.
Impact
A malicious workspace agent can advertise arbitrary AllowedIPs prefixes including another agent's tailnet address. Coder's ServerTailnet routes to agents by tailnet IP so an agent that claims a victim's prefix can intercept web terminal and workspace app traffic and serve spoofed content. Exploitation requires an authenticated user with a running workspace and a modified agent binary.
Patches
The fix validates each AllowedIPs prefix against the authenticating agent's UUID just like Addresses.
The fix was backported to all supported release lines:
| Release line | Patched version |
|---|---|
| 2.34 | v2.34.2 |
| 2.33 | v2.33.8 |
| 2.32 | v2.32.7 |
| 2.29 (ESR) | v2.29.17 |
Workarounds
Operators who cannot upgrade immediately should monitor coordinator logs for agents advertising unexpected AllowedIPs prefixes.
Resources
- Fix: #26144
Credits
Coder would like to thank Anthropic's Security Team (ANT-2026-22451) for independently disclosing this issue!
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| github.com/coder/coder | all versions |
No fix yet |
| github.com/coder/coder/v2 | >= 2.34.0, < 2.34.2 |
2.34.2 |
| github.com/coder/coder/v2 | >= 2.33.0, < 2.33.8 |
2.33.8 |
| github.com/coder/coder/v2 | >= 2.30.0, < 2.32.7 |
2.32.7 |
| github.com/coder/coder/v2 | < 2.29.17 |
2.29.17 |
| github.com/coder/coder/v2 | < 2.29.17>= 2.30.0, < 2.32.7>= 2.33.0, < 2.33.8>= 2.34.0, < 2.34.2 |
2.29.172.32.72.33.82.34.2 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
github.com/coder/coder/v2 Go → 2.34.2
- go
go get github.com/coder/coder/v2@v2.34.2 && go mod tidy
Severity breakdown
CVSS 3.1 8.2
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- None
Weakness
CWE-285: Improper Authorization
The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.
How to prevent it
- Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Architecture and Design: Ensure that you perform access control checks related to your business logic. These checks may be different than the access control checks that you apply to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor.
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
- Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
- System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.
CWE-863: Incorrect Authorization
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
How to prevent it
- Architecture and Design: Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Architecture and Design: Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor [REF-7].
- Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
- Architecture and Design: For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page. One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.
- System Configuration, Installation: Use the access control capabilities of your operating system and server environment and define your access control lists accordingly. Use a "default deny" policy when defining these ACLs.
References
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-h58c-xccx-75m3 Coder: Stored HTML injection via unescaped ApplicationName and LogoURL appearance settings | Medium | Also affects github.com/coder/coder |
| GHSA-8fxq-53rx-ph5f Coder: Login endpoint user enumeration via timing-defense placeholder in password comparison | Medium | Also affects github.com/coder/coder |
| GHSA-qrwj-vh9x-gw5v Coder's workspace agent API insecure redirect handling allowed cross-agent file read and write | High | Also affects github.com/coder/coder |
| GHSA-5wg6-jmq2-53pw Coder's workspace app CORS origin check can be bypassed via UUID-based subdomain spoofing | Medium | Also affects github.com/coder/coder |
| GHSA-7qw2-f75v-62f7 Coder vulnerable to stored HTML injection via workspace agent logs in AgentLogLine component | Medium | Also affects github.com/coder/coder |
| GHSA-84rm-42xw-mx52 Coder's AI Bridge Proxy skips TLS certificate verification in default configuration | High | Also affects github.com/coder/coder |
| GHSA-wqxv-w64v-5wh6 Suspended Coder users retain access to AI Bridge LLM proxy endpoints | Medium | Also affects github.com/coder/coder |
| GHSA-f5vp-w269-392g Coder vulnerable to denial of service via unbounded request body in AI Bridge provider endpoints | Medium | Also affects github.com/coder/coder |
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