CVE-2026-46395

EUVD-2026-34886 · Published May 19, 2026

HAXcms: Private Key Disclosure via Broken HMAC Implementation

Summary

The hmacBase64() function in the HAXcms Node.js backend contains two critical cryptographic implementation errors that together allow any unauthenticated attacker to extract the system’s private signing key and forge arbitrary admin-level JSON Web Tokens (JWTs) allowing them to get full admin access with a single HTTP request.

Details

Bug 1: Hardcoded HMAC Key (line 2160): The function passes the literal string "0" as the HMAC signing key instead of the key parameter, making every HAXcms instance compute identical HMACs for the same input.

Bug 2: Private Key Appended to Output (lines 2161- 2163): After computing the HMAC, the function concatenates the real key parameter which is "this.privateKey + this.salt", the system’s master signing secret is directly onto the output. The combined buffer is base64-encoded and returned as the token.

Every base64url token produced has the same structure: 32 bytes HMAC keyed with "0" and N bytes of privateKey+salt. An attacker base64-decodes any token, discards the first 32 bytes, and reads the private key directly.

The /system/api/connectionSettings endpoint is unauthenticated and returns multiple tokens generated by this function. A single GET request to this endpoint exposes the private key.

The PHP backend (HAXCMS.php:1619-1631) implements this function correctly with the actual key and returns only the hash. The PHP version produces 44-character tokens whereas the broken Node.js version produces 139+ character tokens.

PoC

GET request to /system/api/connectionSettings endpoint and fetch the token.
Extract the private key from the fetched token. The hmacBase64() function produces 32 bytes with HMAC-SHA256 with hardcoded key "0" and the rest of the bytes are privateKey+salt (plaintext). Decode the Base64 token, discard the first 32 bytes, read the remaining bytes as UTF-8 (this is your extracted private key).
Since JWT's are signed with privateKey+salt, use this stolen private key to forge a JWT for admin using JWT.sign(payload, this.privateKey+this.salt). NOTE: the payload uses {id, user (set this as admin), iat (current timestamp), exp (expiration timestamp)}
The same key can also be used to create other tokens (user_token, base_token, form_token, etc).
Use these forged tokens to hit all authenticated endpoints (modify/delete/create etc) with admin privileges.

Impact

An unauthenticated attacker can perform the complete attack chain with a single HTTP request:

Extract private key: GET "/system/api/connectionSettings", base64-decode any token, discard first 32 bytes.
Forge admin JWT: sign arbitrary JWT payloads with the stolen privateKey+salt.
Forge all request tokens: compute valid user_token, site_token for any API call.
Full admin access: create/modify/delete sites, upload files, modify content.

This works even if the admin has changed the default credentials to a strong password. The forged tokens produce no login events in logs.

Technologies

Haxtheweb Haxcms-Nodejs

Weaknesses

CWE-321CWE-200CWE-327

MITRE ATT&CK

Inferred

Where this vulnerability fits in an attack

ReconImpact

Initial Access Stealth Defense Impairment

T1190Exploit Public-Facing Application T1036.001Invalid Code Signature T1553.002Code Signing

References

Potentially impacted assets

See if this affects your attack surface

Latest trending attack

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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.