---
id: "CVE-2026-123660"
page: "https://infrastack.ai/live/CVE-2026-123660"
kind: "vulnerability"
aliases: ["CVE-2026-123660"]
title: "Vulnerability-Lookup: webhook templates can exhaust server memory, causing denial of service"
severity: "medium"
cvss: 5.3
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["package", "python", "self-hosted", "vulnerability-lookup", "webhooks"]
not_affected_if: ["no-webhook-notifications", "registration-disabled", "version-6.4.1-or-later"]
published_at: "2026-11-06T09:17:01+00:00"
first_seen_at: "2026-11-06T09:40:32+00:00"
updated_at: "2026-11-06T09:40:51+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123660", "first_seen_at": "2026-11-06T09:40:32+00:00"}]
exploit_sources: []
---

# Vulnerability-Lookup: webhook templates can exhaust server memory, causing denial of service

Link for people: https://infrastack.ai/live/CVE-2026-123660 (this .md is for agents)

A signed-in user can craft a webhook notification template with an oversized format specifier that makes the server allocate about 1 GB of memory. Repeated placeholders and deep nesting can also exhaust web workers or the notification daemon.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed Vulnerability-Lookup version; affected range is `5.5.1` up to but not including `6.4.1`
- Check whether user self-registration is enabled, since the default configuration lets anyone create an account after e-mail confirmation

## Fix

- Vulnerability-Lookup: upgrade to `6.4.1`, which caps format specifiers at 256, limits rendered templates to 1,000,000 characters, and rejects templates nested deeper than 32 levels

## Timeline

- 2026-11-06T09:40:32+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123660

## Documents

- [fix] Patch: github.com https://github.com/vulnerability-lookup/vulnerability-lookup/commit/2076ffdae3d024649114eeb6fd185338d4bb1f40

## From the sources

In Vulnerability-Lookup 5.5.1 up to but not including 6.4.1, a signed-in user could make the server allocate memory far out of proportion to their input through a webhook notification's payload template. Each placeholder's format specifier was passed unchanged to Python's string formatting, which builds the padded result before its size can be checked. A template of a few dozen bytes, such as {"text": "{title:>999999999}"}, therefore produced a string of about 1 GB when the notification form test-rendered it on save, and repeating such fields multiplied the cost. Templates that passed the save check could also repeat placeholders such as {text} thousands of times; the notification daemon rebuilt those on every webhook delivery. Deeply nested templates raised an unhandled recursion error (HTTP 500). An attacker needs only an account, which the default configuration lets anyone create after e-mail confirmation. They could exhaust the memory of web workers or the notification daemon, causing a denial of service. Version 6.4.1 caps every number in a format specifier at 256, limits a rendered template to 1,000,000 characters both on save and at delivery, and rejects templates nested deeper than 32 levels.

---

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