CVE-2025-53826

EUVD-2025-21540 · Published Jul 16, 2025

File Browser’s insecure JWT handling can lead to session replay attacks after logout

Summary

File Browser’s authentication system issues long-lived JWT tokens that remain valid even after the user logs out. Please refer to the CWE's listed in this report for further reference and system standards. In summary, the main issue is:

Tokens remain valid after logout (session replay attacks)

In this report, I used docker as the documentation instruct:

docker run \
    -v filebrowser_data:/srv \
    -v filebrowser_database:/database \
    -v filebrowser_config:/config \
    -p 8080:80 \
    filebrowser/filebrowser

Details

Issue: Tokens remain valid after logout (session replay attacks)

After logging in and receiving a JWT token, the user can explicitly "log out." However, this action does not invalidate the issued JWT. Any captured token can be replayed post-logout until it expires naturally. The backend does not track active sessions or invalidate existing tokens on logout. Login request:

POST /api/login HTTP/1.1
Host: machine.local:8090
Content-Length: 69

{"username":"admin","password":"password-here","recaptcha":""}

The check found in the code https://github.com/filebrowser/filebrowser/blob/master/http/auth.go is not enough. There is no server-side blacklist or token invalidation on logout. Token renewal and validity only depends on expiry and user store timestamps:

expired := !tk.VerifyExpiresAt(time.Now().Add(time.Hour), true)
updated := tk.IssuedAt != nil && tk.IssuedAt.Unix() < d.store.Users.LastUpdate(tk.User.ID)

PoC

Issue: Tokens remain valid after logout (session replay attacks)

POST /api/login HTTP/1.1
Host: machine.local:8090
Content-Length: 69

{"username":"admin","password":"password-here","recaptcha":""}

Logout in the dashboard. And then try to use the old generated JWT to access any authenticated endpoint eg:

GET /api/resources HTTP/1.1
Host: machine.local:8090
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/138.0.0.0 Safari/537.36
X-Auth: Old-JWT-token-here
Content-Length: 173
Accept: */*
Referer: http://machine.local:8090/files/
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
Content-Length: 26

Connection: keep-alive

Impact

A valid JWT remains active after user logout.
If stolen, tokens persist access indefinitely until expiry.
Violates OWASP Top 10 A2:2021 - Broken Authentication.

Recommendations

Read all CWE's attached in this report
Invalidate JWTs on logout via session store / token blacklist.
Reduce JWT ExpiresAt where possible or use short-lived + refresh tokens.

Technologies

Filebrowser Filebrowser

Weaknesses

CWE-385CWE-305CWE-613CWE-384

References

Potentially impacted assets

See if this affects your attack surface

Latest trending attack

Criticalyesterday

Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)

This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it. Why a second control CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution. Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library. The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support. What this control checks Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service. How to read the result Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside. This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification. Affected and fixed versions Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution. Recommendations Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library. Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli. Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.