CVE-2026-55254: NCalc is a fast, lightweight expression evaluator for .NET

Q: How do I fix CVE-2026-55254?

ncalc: upgrade to 6.1.1. Exact commands for each OS are on this page.

Q: Is CVE-2026-55254 being exploited?

CVE-2026-55254 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-55254 affect?

CVE-2026-55254 affects ncalc. Severity is medium (CVSS 4.8). NCalc is a fast, lightweight expression evaluator for .NET. Prior to 6.1.1, the factorial operator implementation in src/NCalc.Core/Helpers/MathHelper.cs permits specially crafted expressions with extremely large factorial operands, causing

Q: How urgent is CVE-2026-55254?

Priority 22/100. No elevated risk signals yet.

Routine

MEDIUM 4.8UPGRADE

CVE-2026-55254 is a medium-severity flaw (CVSS 4.8) affecting ncalc. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

NCalc is a fast, lightweight expression evaluator for .NET. Prior to 6.1.1, the factorial operator implementation in src/NCalc.Core/Helpers/MathHelper.cs permits specially crafted expressions with extremely large factorial operands, causing excessive CPU consumption or a non-terminating loop due to integer overflow in the factorial calculation logic when applications evaluate untrusted expressions. This issue is fixed in version 6.1.1.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.8 (Medium)
Attack vector	Adjacent network
Attack complexity	High
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 78%)
CISA exploited list	No
Weakness	CWE-190, CWE-770
Published	2026-07-17
Last modified	2026-08-18

Publisher (CNA): GitHub, Inc. · Vendor: ncalc

Last updated 2026-08-18 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-17 20:17 UTCPublished CVE record published
2026-08-18 15:44 UTCUpdated Record last modified

ncalc ncalc UPGRADE

Affected: < 6.1.1

Fixed in: 6.1.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy ncalc || rpm -q ncalc || ncalc --version

2. UPGRADE to 6.1.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade ncalc

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade ncalc

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-55254?

ncalc: upgrade to 6.1.1. Exact commands for each OS are on this page.

Is CVE-2026-55254 being exploited?

CVE-2026-55254 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-55254 affect?

CVE-2026-55254 affects ncalc. Severity is medium (CVSS 4.8). NCalc is a fast, lightweight expression evaluator for .NET. Prior to 6.1.1, the factorial operator implementation in src/NCalc.Core/Helpers/MathHelper.cs permits specially crafted expressions with extremely large factorial operands, causing

How urgent is CVE-2026-55254?

Priority 22/100. No elevated risk signals yet.

References

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