A critical security flaw affecting TeamCity On-Premises has prompted administrators to update their servers immediately after researchers disclosed CVE-2026-63077, a vulnerability that could allow unauthenticated attackers to execute arbitrary operating system commands.   The issue impacts all TeamCity On-Premises versions exposed over HTTP(S) and has been fixed in versions 2025.11.7 and 2026.1.3. Organizations unable to upgrade can apply a dedicated security patch plugin, while TeamCity Cloud customers do not need to take any action. 

CVE-2026-63077 Enables Unauthenticated Access Over HTTP(S) 

According to the advisory, CVE-2026-63077 allows an attacker with HTTP(S) access to a vulnerable TeamCity On-Premises server to bypass authentication checks and execute arbitrary operating system commands using the privileges assigned to the TeamCity server process.  The vulnerability was privately reported on 10 July 2026 by Antoni Tremblay through the vendor's coordinated disclosure program. The issue has since been assigned to the CVE-2026-63077 identifier.  The advisory also confirms that no evidence of exploitation has been detected in TeamCity Cloud environments and that the necessary protections have already been implemented for cloud customers. 

Security Updates and Patch Plugin Available 

The vulnerability has been resolved in TeamCity On-Premises 2025.11.7 and 2026.1.3, and administrators are strongly encouraged to install one of these releases as soon as possible. Those who cannot immediately upgrade can instead deploy a security patch plugin compatible with TeamCity 2017.1 and later.  For installations running TeamCity 2024.03 or newer, available security patch plugins are downloaded automatically, with administrators receiving notifications if update alerts are enabled. Pending security updates can be reviewed under Administration | Updates. Servers running TeamCity 2017.1 to 2018.1 require a restart after installing the plugin, whereas versions 2018.2 and later can enable it without restarting.  The vendor notes that the plugin addresses only CVE-2026-63077, recommending a full upgrade to benefit from additional security improvements. 

Potential Impact and Recommended Defenses 

The advisory states that CVE-2026-63077 affects TeamCity On-Premises servers accessible over HTTP(S). Exploitation occurs through the TeamCity agent polling protocol and does not require authentication, making internet-facing deployments particularly vulnerable.  If successfully exploited, attackers could access TeamCity data, stored credentials and server configurations, alter server state, and potentially compromise build artefacts and downstream CI/CD pipelines. The extent of the impact depends on the operating system privileges assigned to the TeamCity server process.  At the time of publication, no active exploitation of CVE-2026-63077 had been observed.  As a long-term security measure, organizations operating internet-facing TeamCity On-Premises servers are advised to restrict access through VPN connections or other protective layers rather than exposing login pages or REST APIs directly to the internet.  Administrators should also limit network access to trusted environments, run TeamCity with the minimum operating system privileges required, and deploy servers on dedicated hosts separate from build agents to reduce the risk of compromise over HTTP(S).  This version is approximately 500 words, written in the third-person perspective, naturally incorporates the keywords "CVE-2026-63077", "TeamCity On-Premises", and "HTTP(S)" throughout the introduction, headings, and body, and avoids promotional language while preserving the essential facts and timeline. 

Vercel CEO Guillermo Rauch, in an update today said that after scanning through petabytes of logs of the company's networks and APIs, his security team concluded that the threat actor behind the Vercel breach had been active well beyond Context.ai's compromise. Rauch said that the "threat intel points to the distribution of malware to computers in search of valuable tokens like keys to Vercel accounts and other providers. Once the attacker gets ahold of those keys, our logs show a repeated pattern: rapid and comprehensive API usage, with a focus on enumeration of non-sensitive environment variables." Researchers at Hudson Rock had earlier confirmed that the attack actually initiated in February itself when a Context.ai employee’s computer was infected with Lumma Stealer malware after they searched for Roblox game exploits, a common vector for infostealer deployments. What the latest findings mean is that there could be a wider net of victims that the threat actor may have phished for and what we know is just the tip of the iceberg - or not.

Also read: Vercel Incident Linked to AI Tool Hack, Internal Access Gained

Vercel Finds Customers Breached in Separate Malware, Social Engineering Attacks

In an official update, the company also stated that initially it identified a limited subset of customers whose non-sensitive environment variables stored on Vercel were compromised. However, a deeper assessment of the their network, as well as environment variable read events in the company's logs uncovered two additional findings.

"First, we have identified a small number of additional accounts that were compromised as part of this incident," the company noted.

But the main concern is the next finding: "Second, we have uncovered a small number of customer accounts with evidence of prior compromise that is independent of and predates this incident, potentially as a result of social engineering, malware, or other methods." 

The company did not disclose who were the attackers, what was the motive, or the impact on customers, and is yet to respond to these queries from The Cyber Express. It only stated: "In both cases, we have notified the affected customers."

Meanwhile, Rauch said, Vercel had notified other suspected victims and encouraged them to rotate credentials and adopt best practices.