How severe is CVE-2017-9785?

CVE-2017-9785 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2017-9785?

CVE-2017-9785 affects the following packages: Nancy (NuGet), Nancy (NuGet). Ecosystems affected: NuGet.

How do I fix CVE-2017-9785?

Update Nancy to 1.4.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2017-9785 is resolved across your whole dependency graph.

How do I detect CVE-2017-9785 in my NuGet dependencies?

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

How do I mitigate CVE-2017-9785 if there is no patch (or I can't update yet)?

Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Is CVE-2017-9785 actively exploited in the wild?

No public exploit code has been indexed for CVE-2017-9785 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-2017-9785?

CVE-2017-9785 has an EPSS (Exploit Prediction Scoring System) score of 3.0%, placing it in the 87th 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-2017-9785?

CVE-2017-9785 is classified as Deserialization of Untrusted Data (CWE-502). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2017-9785 published, and has it been updated?

CVE-2017-9785 was published on July 20, 2017 and was last updated on October 20, 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

CRITICAL severity

CVE-2017-9785 — Nancy

CRITICAL

CVE-2017-9785 is a critical-severity (CVSS 9.8) Deserialization of Untrusted Data vulnerability in Nancy. A fix is available for Nancy — see the affected versions and patch details below.

Deserialization of Untrusted Data in NancyFX Nancy

Also known asGHSA-mx3q-j2g2-5qxq

Published

Jul 20, 2017

Updated

Oct 20, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

3.0%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs87th percentile — riskier than 87% of all scored CVEsHighest risk

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

.NETNancy.NETNancy

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

Csrf.cs in NancyFX Nancy before 1.4.4 and 2.x before 2.0-dangermouse has Remote Code Execution via Deserialization of JSON data in a CSRF Cookie.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
.NETNuGet	`Nancy`	all versions	1.4.4`dotnet add package Nancy --version 1.4.4`
.NETNuGet	`Nancy`	≥ 2.0.0-alpha&&< 2.0.0	2.0.0`dotnet add package Nancy --version 2.0.0`

Affected Products

1 product · 4 configurations

Application

nancynancyfx

≤ 1.4.3

1 version

2.0.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Nancy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Nancy to 1.4.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2017-9785 is resolved across your whole dependency graph.
Workarounds
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Frequently Asked Questions

Csrf.cs in NancyFX Nancy before 1.4.4 and 2.x before 2.0-dangermouse has Remote Code Execution via Deserialization of JSON data in a CSRF Cookie.

O3 Security · Impact-Aware SCA

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Find it across NuGet, including transitive dependencies.

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CVSS Score

9.8/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Raw vector

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE Classification

CWE-502Deserialization of Untrusted Data

Weaponization

No Nuclei template, Metasploit module or public proof-of-concept found.

Timeline

Disclosed

Jul 20, 2017

Last updated

Oct 20, 2026

Identifiers

CVE-2017-9785

GHSA-mx3q-j2g2-5qxq

References

Advisorygithub.com · v1.4.4 Advisorynvd.nist.gov · CVE 2017 9785

Related vulnerabilities

This CVE is critical severity; 1 of 8 other CVEs with CWE-502 is rated as high or higher (top: critical).

CVE-2026-115878CVE-2026-62848CVE-2026-115912CVE-2026-116580CVE-2026-114608CVE-2026-102554GHSA-673q-mjm6-r5xrCVE-2026-70035Browse all CWE-502

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 20, 2026

CVE-2017-9785 — Nancy

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2017-9785 in your dependencies?