CVE-2026-123660 Vulnerability-Lookup: memory amplification through webhook payload template format specifiers
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-123660?
CVE-2026-123660 is a medium-severity vulnerability in vulnerability-lookup, published on 6 Nov 2026.
Official description
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.
Which versions are affected by CVE-2026-123660?
How do I fix CVE-2026-123660?
No fix has been published for CVE-2026-123660 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-123660 being exploited?
There is no known exploitation of CVE-2026-123660 in the wild and no public exploit code.
Sources
Also known as GHSA-fjqr-7p2w-j9wx.