Vaadin Framework 8: Session lock leak allows denial of service
Summary
Vaadin Framework 8 does not release the session lock when a request contains a non-numeric v-uiId parameter. Every later request to that session then blocks, and repeated requests exhaust the servlet container's thread pool and take the application down. No authentication is required; a session cookie, which any client obtains with one request, is enough. Vaadin Framework 7 and Vaadin 10 and later are not affected.
Affected
- com.vaadin:vaadin-server 8.16.0 to 8.32.1
- com.vaadin:vaadin-server-mpr-jakarta 8.18.0 to 8.32.1
Fixed in
- Upgrade to Vaadin Framework 8.32.2 or later (Vaadin extended maintenance release)
Workaround
- Reject requests whose v-uiId parameter is not an integer before Vaadin handles them, by overriding VaadinServlet.service() and answering HTTP 400.
- Locks that have already leaked are only released by restarting the application.
Exploitation
- Exploited in the wild: no evidence found.
- Public proof of concept: none found.
- CISA SSVC: Exploitation none, automatable yes, technical impact partial.
- The vendor reports that an automated scanner fuzzing the parameter triggered the issue on a production node.
Our recommendation
- Identify all Vaadin 8 applications, including transitive dependencies, by checking vaadin-server and vaadin-server-mpr-jakarta versions in build files and deployed WARs.
- Upgrade affected applications to 8.32.2 or later.
- If an upgrade is not possible now, apply the vendor workaround after testing it in a non-production environment.
- Monitor for thread-pool exhaustion and stuck sessions, and restrict exposure of affected applications where possible.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Vaadin security advisory CVE-2026-110803 vaadin.com
- Vaadin Framework 8.32.2 release notes github.com
- VulDB entry vuldb.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 00:58.
Original description (NVD)
VaadinService.requestEnd() in Vaadin Framework 8 locks the session and then reads the v-uiId request parameter outside the block that releases the lock. A request carrying a non-numeric v-uiId makes Integer.parseInt throw while the session lock is held, so the lock is never released and the container thread returns to its pool still owning it. Every later request to that session then blocks forever in VaadinService.lockSession(), and repeating the request exhausts the thread pool and takes the application down. No authentication is required: a session cookie, which any client obtains with a single request, is enough. Vaadin 10 and later are not affected, because Flow releases the lock in a finally block and does not read that parameter there, and Vaadin Framework 7 is not affected either. Users of affected versions should apply the following mitigation or upgrade. Releases that have fixed this issue include: Product version Vaadin Framework 8.16.0 - 8.32.1 Mitigation Upgrade to 8.32.2 Vaadin Framework 7 and Vaadin 10 and later do not carry this behaviour and need no upgrade for this issue. Artifacts Maven coordinates / Vulnerable versions / Fixed version com.vaadin:vaadin-server / 8.16.0 - 8.32.1 / >=8.32.2 com.vaadin:vaadin-server-mpr-jakarta / 8.18.0 - 8.32.1 / >=8.32.2
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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