Scriban: Denial of Service via Unbounded Cumulative Template Output Bypassing LimitToString

Exploitation

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

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:L/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 LimitToString safety limit (default 1MB since commit b5ac4bf) can be bypassed to allocate approximately 1GB of memory by exploiting the per-call reset of currentToStringLength in ObjectToString. Each template expression rendered through TemplateContext.Write(SourceSpan, object) triggers a separate top-level ObjectToString call that resets the length counter to zero, and the underlying StringBuilderOutput has no cumulative output size limit. An attacker who can supply a template can cause an out-of-memory condition in the host application. Details The root cause is in TemplateContext.Helpers.cs, in the ObjectToString method: Each time a template expression is rendered, TemplateContext.Write(SourceSpan, object) calls ObjectToString: The StringBuilderOutput.Write method appends unconditionally with no size check: Execution flow: 1. Template creates a string of length 1,048,575 (one byte under the 1MB LimitToString default) 2. A for loop iterates up to LoopLimit (default…

Published by the source

24 Mar 2026, 22:15 UTC

Last modified by the source

6 Jul 2026, 13:09 UTC

Source last checked

26 Oct 2026, 17:05 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-m2p3-hwv5-xpqw

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# Patch Next advisory brief: GHSA-m2p3-hwv5-xpqw

Advisory: Scriban: Denial of Service via Unbounded Cumulative Template Output Bypassing LimitToString
IDs: GHSA-m2p3-hwv5-xpqw
Record: https://patchnext.com/advisories/ghsa-m2p3-hwv5-xpqw (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: Medium (CVSS 6.5)
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-m2p3-hwv5-xpqw (GitHub-reviewed advisory GHSA-m2p3-hwv5-xpqw lists affected ranges: NuGet scriban >=0 =0 <7.0.0)

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