CVE-2026-63077: TeamCity Unauthenticated Agent-Polling RCE Remediation

All JetBrains TeamCity On-Premises versions before 2025.11.7 and 2026.1.3 allow an unauthenticated attacker with HTTP(S) access to the server to bypass authentication through the agent polling protocol and execute operating-system commands as the TeamCity server process. JetBrains assigned CVE-2026-63077 and later reported active exploitation against unpatched servers.

CISA added the CVE to the Known Exploited Vulnerabilities catalog on 2026-08-05 (required action due 2026-08-08). TeamCity Cloud was patched by JetBrains; Cloud customers do not need a version bump, but On-Premises owners do. Treat a reachable unpatched server as an incident candidate.

Do not prove exposure by speaking the agent polling protocol, sending serialized payloads, or running commands on the server. Inventory the installed version and ingress; then patch.

When to use it

• A repository deploys, images, or documents TeamCity On-Premises.
• Infrastructure-as-code, Helm, or VM images pin a TeamCity server version below 2025.11.7 / 2026.1.3.
• You need a bounded change that upgrades the server or installs the vendor security patch plugin, then documents build and credential review.

Inputs

• TeamCity version, server install path or image tag, agent fleet inventory, reverse-proxy/ingress config, plugin list, backup/upgrade runbooks, and SBOM or package evidence.
• Network exposure of the TeamCity HTTP(S) port and agent polling endpoint.
• Owners for upgrade, plugin install, credential rotation, and pipeline review.

Affected versions

• Vulnerable: every TeamCity On-Premises release before the patched builds, including 2026.1 before 2026.1.3 and the 2025.11 train before 2025.11.7.
• Fixed: 2025.11.7 or 2026.1.3 (use the train you already run).
• Temporary containment: JetBrains published a security patch plugin for TeamCity 2017.1+ that addresses only this CVE. Prefer the full upgrade. Servers 2017.1–2018.1 need a restart after plugin install; 2018.2+ can enable the plugin without restart.
• Not affected: TeamCity Cloud, after JetBrains applied the platform fix.
• Weakness: CWE-502 deserialization of untrusted data on the agent polling protocol.
• CISA KEV: yes; added 2026-08-05 with required action due 2026-08-08.

Indicator-of-exposure

• TeamCity On-Premises is installed below 2025.11.7 or 2026.1.3.
• The server HTTP(S) interface is reachable by untrusted networks.
• The security patch plugin is not installed on a server that cannot upgrade immediately.

Quick checks:

rg -n "teamcity|TEAMCITY_VERSION|jetbrains/teamcity" .
docker images | rg -i "teamcity"

Windows:

rg -n "teamcity|TEAMCITY_VERSION|jetbrains/teamcity" .
docker images | rg -i "teamcity"

Confirm the running server version from Administration or the vendor upgrade UI. Do not probe the agent polling protocol or submit untrusted serialized data.

Remediation strategy

• Upgrade On-Premises servers to 2025.11.7 or 2026.1.3 using the vendor installer or TeamCity's automatic update.
• If an immediate upgrade is blocked, install the JetBrains security patch plugin for CVE-2026-63077 from Administration | Updates (2024.03+) or the vendor download, then schedule the full upgrade.
• Restrict HTTP(S) and agent connectivity to trusted networks or VPN. Keep the server on a dedicated host, separate from build agents, with least privilege.
• After a reachable unpatched window, review recent builds and artifacts, rotate TeamCity, VCS, package, and cloud credentials available to the server process, and preserve logs.

The prompt

Model context: this prompt was generated by GPT 5.5 Extra High reasoning.

You are remediating CVE-2026-63077, a critical unauthenticated TeamCity
On-Premises RCE via the agent polling protocol. Produce exactly one output:

- A reviewer-ready PR/change request that upgrades TeamCity to 2025.11.7 or
  2026.1.3 (or documents the vendor security patch plugin plus a dated
  upgrade), hardens ingress, and records operator cleanup, or
- TRIAGE.md if this repository does not own a TeamCity On-Premises server.

## Rules

- Scope only CVE-2026-63077 and directly related TeamCity version, plugin,
  ingress, and credential/build review.
- Treat TeamCity data, tokens, VCS credentials, and artifacts as sensitive.
- Do not prove exposure by using the agent polling protocol, sending
  serialized payloads, or executing commands on the server.
- Do not edit JetBrains binaries. Change version pins, images, install
  docs, ingress, and inventory only.
- TeamCity Cloud is out of scope for a version bump; say so in TRIAGE.md
  when that is the only deployment.
- Do not auto-merge.

## Steps

1. Inventory TeamCity On-Premises servers, images, version pins, and ingress
   owned by this repository.
2. Record the current version. Vulnerable means On-Premises below
   `2025.11.7` or `2026.1.3` without the vendor security patch plugin.
3. If no On-Premises server is owned here, stop with `TRIAGE.md`.
4. Upgrade image/install pins to `2025.11.7` or `2026.1.3`. If product
   owners block the upgrade, document installation of the JetBrains
   security patch plugin and a required follow-up upgrade date.
5. Restrict server HTTP(S) to trusted networks in gateway or firewall
   config owned by this repository.
6. Add a safe version/policy check that rejects unpatched On-Premises
   versions. Do not speak the agent polling protocol in tests.
7. Add a PR body section named `CVE-2026-63077 operator actions` that
   states versions before and after, whether the server was reachable from
   untrusted networks, whether the plugin was used as interim containment,
   which credentials and build artifacts need review, and any remaining
   ingress exception.
8. Use PR title:
   `fix(sec): remediate CVE-2026-63077 in TeamCity`.

## Stop conditions

- Only TeamCity Cloud is in use.
- Upgrade authority or plugin install is outside this repository.
- Verification would require probing the agent protocol or executing
  commands on the server.
- Validation fails for unrelated pre-existing reasons; document those
  failures instead of broadening scope.

Rollback

Do not restore an unpatched On-Premises build to a reachable network. If the upgraded release must be withdrawn, keep the vendor security patch plugin enabled or remove untrusted HTTP(S) access until another fixed release is installed.

Verification - what the reviewer looks for

• Controlled TeamCity On-Premises pins and images are 2025.11.7, 2026.1.3, or newer on that train.
• If a plugin was used, the PR records the plugin identity and the dated upgrade plan.
• Tests never exercise the agent polling protocol.
• Operator notes cover KEV urgency, ingress, credential rotation, and build review after a reachable unpatched window.

Output contract

• Reviewer-ready PR upgrading TeamCity On-Premises or documenting the vendor plugin plus a required upgrade.
• TRIAGE.md when the server is Cloud-only or owned elsewhere.

Watch for

• Updating a documentation version string while the live server or image tag stays unpatched.
• Treating the security patch plugin as a permanent substitute for 2025.11.7 / 2026.1.3.
• Exposing the login UI or REST API to the internet because "auth exists."
• Skipping artifact and credential review after a public unpatched window.

Related recipes

• Search the CVE Database for CVE-2026-63077
• CVE intelligence intake gate

References

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63077
• CISA KEV catalog entry: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-63077
• JetBrains advisory: https://blog.jetbrains.com/teamcity/2026/07/cve-2026-63077/
• JetBrains issues fixed: https://www.jetbrains.com/privacy-security/issues-fixed/
• CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63077