How severe is CVE-2026-55254?

CVE-2026-55254 has a CVSS score of 4.8/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-55254?

CVE-2026-55254 affects the following packages: NCalc.Core (NuGet), NCalcSync (NuGet). Ecosystems affected: NuGet.

How do I fix CVE-2026-55254?

Update NCalc.Core to 6.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55254 is resolved across your whole dependency graph.

How do I detect CVE-2026-55254 in my NuGet dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for NCalc.Core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-55254 if there is no patch (or I can't update yet)?

Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Is CVE-2026-55254 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-55254 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-55254?

CVE-2026-55254 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 21th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-55254?

CVE-2026-55254 is classified as CWE-190 (CWE-190), CWE-770 (CWE-770). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-55254 published, and has it been updated?

CVE-2026-55254 was published on July 17, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

.NET

.NET NuGet

Not in CISA KEV

MEDIUM severity

CVE-2026-55254 — NCalc.Core

MEDIUMFix: ncalc/ncalc@eeb6155

CVE-2026-55254 is a medium-severity (CVSS 4.8) CWE-190 vulnerability in NCalc.Core. A fix is available for NCalc.Core — see the affected versions and patch details below.

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

Also known asGHSA-3w5p-95mh-gq75

Published

Jul 17, 2026

Updated

Oct 21, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-55254.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs21th percentile — riskier than 21% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-55254 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 397,508 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected

.NETNCalc.Core.NETNCalcSync

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.

Description

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:

99999999999999!
9223372036854775807!
1.5e16!

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 reject factorial operations on large values.
Implement execution time limits, request timeouts, or cancellation mechanisms around expression evaluation.

These mitigations may reduce exposure but do not fully address the underlying vulnerability.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
.NETNuGet	`NCalc.Core`	all versions	6.1.1`dotnet add package NCalc.Core --version 6.1.1`
.NETNuGet	`NCalcSync`	all versions	6.1.1`dotnet add package NCalcSync --version 6.1.1`

Affected Products

1 product · 1 configurations

Application

ncalcncalc

< 6.1.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for NCalc.Core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update NCalc.Core to 6.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55254 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Frequently Asked Questions

### 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: ```tex