NCalc: Denial of Service via Unbounded and Non-Terminating Factorial Evaluation

Exploitation

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

CVSS

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

EPSS

• CVE-2026-55254: 0.29% estimated exploitation activity in the next 30 days; percentile 21.80 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact A denial-of-service (DoS) vulnerability exists in the factorial operator implementation of NCalc. Specially crafted expressions containing extremely large factorial operands can trigger excessive CPU consumption or cause evaluation to enter a non-terminating loop due to integer overflow in the factorial calculation logic. Applications that evaluate untrusted expressions using affected versions of NCalc may be vulnerable to resource exhaustion, potentially resulting in service disruption or application unresponsiveness. This issue can be triggered with expressions such as: Patches The vulnerability has been fixed by adding bounds validation for factorial operands and rejecting unsupported values before evaluation. Users should upgrade to the first release containing the fix from pull request #575. (v6.1.1+) Workarounds If upgrading is not immediately possible: Do not evaluate expressions originating from untrusted users. Validate or sanitize expressions before evaluation and…

Published by the source

18 Jun 2026, 13:05 UTC

Last modified by the source

18 Jun 2026, 13:05 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-3w5p-95mh-gq75

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# Patch Next advisory brief: CVE-2026-55254

Advisory: NCalc: Denial of Service via Unbounded and Non-Terminating Factorial Evaluation
IDs: CVE-2026-55254, GHSA-3w5p-95mh-gq75
Record: https://patchnext.com/advisories/cve-2026-55254 (revision 1, source checked 26 Oct 2026, 17:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ncalc.core 6.1.1; ncalcsync 6.1.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet ncalc.core: affected < 6.1.1; fixed in 6.1.1
- NuGet ncalcsync: affected < 6.1.1; fixed in 6.1.1

## Suggested inspection (read-only)
- NuGet ncalc.core: check the installed version with your package manager.
- NuGet ncalcsync: 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 ncalc.core, ncalcsync.
- 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-3w5p-95mh-gq75 (GitHub-reviewed advisory GHSA-3w5p-95mh-gq75 lists affected ranges: NuGet ncalc.core >=0 =0 <6.1.1)

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