CVE-2026-120326: Vaadin file name spoofing in downloads

Summary

Vaadin Flow applications that pass untrusted file names to `DownloadEvent.setFileName` or `inline` let an attacker make the browser save a download under a file name and extension of their choosing, bypassing the application's name or extension restrictions. An attacker can reach this remotely with low-privilege login, but a user must take an action such as starting the download.

Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.

Read the original description

DownloadEvent.setFileName(String) in Vaadin Flow writes the download file name into the Content-Disposition header without escaping it. When the name is pure US-ASCII the header is built as attachment; filename="<name>" with the name inserted verbatim, so a double quote in the name ends the quoted string early and the rest of the name is read by the browser as further header parameters. The inline(String) variant, present from Vaadin 25.0, builds the name the same way. An application that passes an untrusted file name to either method, for example when re-serving a file under the name it was uploaded with, lets an attacker add a filename* parameter. Browsers prefer filename* over filename, so the file is saved under a name and extension of the attacker's choosing, which defeats any file name or extension restriction the application enforces. The attacker cannot change the attachment or inline disposition itself and cannot split the header.

Users of affected versions should apply the following mitigation or upgrade. Releases that have fixed this issue include:

Product version Vaadin 24.8.0 - 24.8.17 Vaadin 24.9.0 - 24.9.25 Vaadin 24.10.0 - 24.10.13 Vaadin 25.0.0 - 25.0.13 Vaadin 25.1.0 - 25.1.13 Vaadin 25.2.0 - 25.2.12 Vaadin 25.3.0 - 25.3.4

Mitigation No fixed release on this line, upgrade to 24.9.26 or newer Upgrade to 24.9.26 Upgrade to 24.10.14 No fixed release on this line, upgrade to 25.2.13 or newer No fixed release on this line, upgrade to 25.2.13 or newer Upgrade to 25.2.13 Upgrade to 25.3.5

Vaadin versions below 24.8 are not affected: the DownloadEvent API does not exist in them.

cve.now Index

18Pcve.now Index 18 of 100 · methodology v3 · provisional

Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
Exposure3/25Reachable over the network · Unknown: No advisory context yet
Reach10/20Affects Maven packages
Severity4.8/10CVSS 4.8
No patch0/5No signal

What would change the score

Would score about 73 if added to CISA KEV
Would score about 68 if CISA's SSVC rates exploitation active
Would score about 37 if advisories confirm default setups are exposed

How the score works · Rankings

What to do

Upgrade to a fixed version: com.vaadin:vaadin 24.9.26, 24.10.14, 25.2.13, 25.3.5 · com.vaadin:vaadin-core 24.9.26, 24.10.14, 25.2.13, 25.3.5 · com.vaadin:flow-server 24.9.31, 24.10.17, 25.2.16, 25.3.6.

Check your systems with an agent

Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.

Check whether my systems are affected by CVE-2026-120326 (Unescaped Download File Name Allows Content-Disposition Parameter Injection in Vaadin Flow), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-120326 (entry last updated 2026-11-10):
Affected:
- Maven package com.vaadin:vaadin: from 24.8.0, through 24.8.17; from 24.9.0, fixed in 24.9.26; from 24.10.0, fixed in 24.10.14; from 25.0.0, through 25.0.13; from 25.1.0, through 25.1.13; from 25.2.0, fixed in 25.2.13; from 25.3.0, fixed in 25.3.5
- Maven package com.vaadin:vaadin-core: from 24.8.0, through 24.8.17; from 24.9.0, fixed in 24.9.26; from 24.10.0, fixed in 24.10.14; from 25.0.0, through 25.0.13; from 25.1.0, through 25.1.13; from 25.2.0, fixed in 25.2.13; from 25.3.0, fixed in 25.3.5
- Maven package com.vaadin:flow-server: from 24.8.0, through 24.8.16; from 24.9.0, fixed in 24.9.31; from 24.10.0, fixed in 24.10.17; from 25.0.0, through 25.0.15; from 25.1.0, through 25.1.19; from 25.2.0, fixed in 25.2.16; from 25.3.0, fixed in 25.3.6
Fixed versions: 24.9.26, 24.10.14, 25.2.13, 25.3.5, 24.9.31, 24.10.17, 25.2.16, 25.3.6.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-120326 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-120326 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Packages (Maven): find every lockfile in each project and run check_stack from the cve.now MCP server on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://vaadin.com/security/cve-2026-120326
- https://github.com/vaadin/flow/pull/26704
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-120326
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-120326.

Timeline

Nov 10, 2026, 11:49 AM UTCCVE published
Nov 10, 2026, 11:53 AM UTCFirst seen by cve.now

Affected versions

com.vaadin:vaadinMaven
From 24.8.0 · through 24.8.17; From 24.9.0 · fixed in 24.9.26; From 24.10.0 · fixed in 24.10.14; From 25.0.0 · through 25.0.13; From 25.1.0 · through 25.1.13; From 25.2.0 · fixed in 25.2.13; From 25.3.0 · fixed in 25.3.5
com.vaadin:vaadin-coreMaven
From 24.8.0 · through 24.8.17; From 24.9.0 · fixed in 24.9.26; From 24.10.0 · fixed in 24.10.14; From 25.0.0 · through 25.0.13; From 25.1.0 · through 25.1.13; From 25.2.0 · fixed in 25.2.13; From 25.3.0 · fixed in 25.3.5
com.vaadin:flow-serverMaven
From 24.8.0 · through 24.8.16; From 24.9.0 · fixed in 24.9.31; From 24.10.0 · fixed in 24.10.17; From 25.0.0 · through 25.0.15; From 25.1.0 · through 25.1.19; From 25.2.0 · fixed in 25.2.16; From 25.3.0 · fixed in 25.3.6

Evidence 4

Vendor advisory · 1

Establishes: Affected and fixed versions.

Link
vaadin.com · security/cve-2026-120326

CVE record · 2

Establishes: The identifier and description.

Record
CVE List · CVE-2026-120326
Record
NVD · CVE-2026-120326

Corrections

None so far.

Something wrong on this page? Report an error. Every fix is listed here.

Questions about CVE-2026-120326

Is CVE-2026-120326 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data

Which versions are affected by CVE-2026-120326?

com.vaadin:vaadin (Maven): from 24.8.0 through 24.8.17; from 24.9.0 before 24.9.26; from 24.10.0 before 24.10.14; from 25.0.0 through 25.0.13; from 25.1.0 through 25.1.13; from 25.2.0 before 25.2.13; from 25.3.0 before 25.3.5. com.vaadin:vaadin-core (Maven): from 24.8.0 through 24.8.17; from 24.9.0 before 24.9.26; from 24.10.0 before 24.10.14; from 25.0.0 through 25.0.13; from 25.1.0 through 25.1.13; from 25.2.0 before 25.2.13; from 25.3.0 before 25.3.5. com.vaadin:flow-server (Maven): from 24.8.0 through 24.8.16; from 24.9.0 before 24.9.31; from 24.10.0 before 24.10.17; from 25.0.0 through 25.0.15; from 25.1.0 through 25.1.19; from 25.2.0 before 25.2.16; from 25.3.0 before 25.3.6.Source: cve.now feed data

How do I fix CVE-2026-120326?

Upgrade to a fixed version: com.vaadin:vaadin 24.9.26, 24.10.14, 25.2.13, 25.3.5 · com.vaadin:vaadin-core 24.9.26, 24.10.14, 25.2.13, 25.3.5 · com.vaadin:flow-server 24.9.31, 24.10.17, 25.2.16, 25.3.6.Source: cve.now feed data

Unescaped Download File Name Allows Content-Disposition Parameter Injection in Vaadin Flow