Scriban: Uncontrolled Memory Allocation via string.pad_left/pad_right Allows Remote Denial of Service

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary The built-in string.padleft and string.padright template functions in Scriban perform no validation on the width parameter, allowing a template expression to allocate arbitrarily large strings in a single call. When Scriban is exposed to untrusted template input — as in the official Scriban.AppService playground deployed on Azure — an unauthenticated attacker can trigger ~1GB memory allocations with a 39-byte payload, crashing the service via OutOfMemoryException. Details StringFunctions.PadLeft and StringFunctions.PadRight (src/Scriban/Functions/StringFunctions.cs:1181-1203) directly delegate to .NET's String.PadLeft(int) / String.PadRight(int) with no bounds checking: The TemplateContext.LimitToString property (default 1MB, set at TemplateContext.cs:147) does not prevent the allocation. This limit is only checked during ObjectToString() conversion (TemplateContext.Helpers.cs:101-103), which runs after the string has been fully allocated by PadLeft/PadRight. The dangerous…

Published by the source

24 Mar 2026, 22:13 UTC

Last modified by the source

6 Jul 2026, 13:08 UTC

Source last checked

26 Oct 2026, 17:05 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-v66j-x4hw-fv9g

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: GHSA-v66j-x4hw-fv9g

Advisory: Scriban: Uncontrolled Memory Allocation via string.pad_left/pad_right Allows Remote Denial of Service
IDs: GHSA-v66j-x4hw-fv9g
Record: https://patchnext.com/advisories/ghsa-v66j-x4hw-fv9g (revision 1, source checked 26 Oct 2026, 17:05 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: scriban.signed 7.0.0; scriban 7.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet scriban.signed: affected < 7.0.0; fixed in 7.0.0
- NuGet scriban: affected < 7.0.0; fixed in 7.0.0

## Suggested inspection (read-only)
- NuGet scriban.signed: check the installed version with your package manager.
- NuGet scriban: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on scriban.signed, scriban.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-v66j-x4hw-fv9g (GitHub-reviewed advisory GHSA-v66j-x4hw-fv9g lists affected ranges: NuGet scriban >=0 =0 <7.0.0)

Commands are suggestions: review each one before running it.