CVE-2026-63077: JetBrains TeamCity Deserialization of Untrusted Data Vulnerability

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Yes, if you run JetBrains TeamCity. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-08-05, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-08-08; treat that as the outer limit, not the target. CISA also lists it as known to be used in ransomware campaigns.
• EPSS 89.6%, percentile 99.8: FIRST’s model estimates a 89.6% chance of exploitation activity in the next 30 days, higher than 99.8% of all scored CVEs (very high). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Editorial verdict: Act now. TeamCity CVE-2026-63077: Unauthenticated RCE, Exploited — Any self-hosted TeamCity server below 2025.11.7 or 2026.1.3 that an attacker can reach over HTTP(S) can be taken over without credentials, and ransomware crews are using it; patch or apply the security patch plugin today, then check for intrusions.

What it is

In JetBrains TeamCity before 2026.1.3, 2025.11.7 unauthenticated remote code execution was possible via the agent polling protocol

CISA’s summary

JetBrains TeamCity contains a deserialization of untrusted data vulnerability that could allow unauthenticated remote code execution via the agent polling protocol.

Weakness type: CWE-502.

Product: JetBrains TeamCity · Assigned by: JetBrains · Published: 2026-07-27

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: added 2026-08-05; federal due date 2026-08-08. Known ransomware use: Known.
• CISA required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
• CISA SSVC assessment: exploitation active, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 89.57% probability of exploitation activity in the next 30 days; percentile 99.8.

Timeline

• 2026-07-27 — CVE record published by JetBrains
• 2026-07-27 — erroneo.us brief: TeamCity CVE-2026-63077: Unauthenticated RCE, Exploited
• 2026-08-05 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2026-08-08 — CISA remediation deadline for US federal agencies
• 2026-09-23 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Listed in CISA KEV notes (blog.jetbrains.com) blog.jetbrains.com
2. Listed in CISA KEV notes (jetbrains.com) jetbrains.com

Vulnerability records

1. CVE.org record CVE-2026-63077 cve.org
2. NVD entry CVE-2026-63077 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov
2. Listed in CISA KEV notes (cisa.gov) cisa.gov
3. Listed in CISA KEV notes (cisa.gov) cisa.gov

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