How severe is CVE-2026-59859?

No CVSS score has been assigned to CVE-2026-59859 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-59859?

CVE-2026-59859 affects the following packages: Microsoft.OpenApi.Kiota (NuGet), Microsoft.OpenApi.Kiota.Builder (NuGet), Microsoft.OpenApi.Kiota (NuGet), Microsoft.OpenApi.Kiota.Builder (NuGet). Ecosystems affected: NuGet.

How do I fix CVE-2026-59859?

Update Microsoft.OpenApi.Kiota to 1.32.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59859 is resolved across your whole dependency graph.

How do I detect CVE-2026-59859 in my NuGet dependencies?

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

How do I mitigate CVE-2026-59859 if there is no patch (or I can't update yet)?

Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Is CVE-2026-59859 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-59859 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-2026-59859?

CVE-2026-59859 has an EPSS (Exploit Prediction Scoring System) score of 1.4%, placing it in the 72th 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-2026-59859?

CVE-2026-59859 is classified as Code Injection (CWE-94). 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-2026-59859 published, and has it been updated?

CVE-2026-59859 was published on July 16, 2026 and was last updated on October 7, 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 NuGet

Not in CISA KEV

CVE-2026-59859 — Microsoft.OpenApi.Kiota

Fix: microsoft/kiota@5e2a211

CVE-2026-59859 is a Code Injection vulnerability in Microsoft.OpenApi.Kiota. A fix is available for Microsoft.OpenApi.Kiota — see the affected versions and patch details below.

Kiota: Code Generation Literal Injection in the PHP Generator

Also known asGHSA-jqwh-526h-c92j

Published

Jul 16, 2026

Updated

Oct 7, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Oct 17, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
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-2026-59859.

EPSS Exploitation Probability

via FIRST.org ↗

1.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs72th percentile — riskier than 72% of all scored CVEsHighest risk

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

Real-World Exposure

4 pkgs affected

.NETMicrosoft.OpenApi.Kiota.NETMicrosoft.OpenApi.Kiota.Builder.NETMicrosoft.OpenApi.Kiota.NETMicrosoft.OpenApi.Kiota.Builder

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

The Kiota PHP code generator is vulnerable to a code generation literal injection attack. The generator embeds string values from OpenAPI fields (e.g. description, default values, and property names) directly into PHP double-quoted string literals without properly escaping the $ character. Since PHP evaluates string interpolation expressions like "${expr}", "$var", and "{$obj->prop}" within double-quoted strings at runtime, an attacker who controls an OpenAPI specification file can inject arbitrary PHP code into generated model and request-builder classes.

Who is impacted

Developers using Kiota to generate PHP API clients from external or untrusted OpenAPI specifications

Teams with CI/CD pipelines configured to automatically regenerate client code from remote specs

Applications that deploy generated PHP code to production servers

Vulnerability details

Affected component: StringExtensions.cs

Root cause: The shared SanitizeDoubleQuote() function in Writers/StringExtensions.cs does not escape the $ character. As a result, any schema-derived string emitted as a PHP double-quoted literal preserves $-prefixed interpolation constructs (${...}, $var, {$...}) verbatim, which PHP evaluates at runtime instead of treating as literal text. This is the same class of code-generation literal-injection flaw previously fixed for the Ruby generator (# interpolation), recurring here as a missed variant for PHP's $ interpolation in the sibling sanitizer helper.

Attack vectors

OpenAPI description and default fields in schema properties

Property wire-name keys embedded in deserializer/serializer methods

Any schema-derived string embedded in PHP double-quoted literals

Severity: Critical when generated code reaches production; High for CI/CD environments with access to production secrets; Medium for public third-party specs; Low for developer-controlled specs.

Patches

#7863

Workarounds

If you cannot upgrade immediately:

Audit and sanitize OpenAPI specifications: Review all OpenAPI specification files for any descriptions, default values, or property names containing the $ character. Remove or replace any suspicious strings before code generation.
Code review of generated files: Implement mandatory code review of all generated PHP files before merging into any branch. Look for double-quoted strings containing ${, $var, or {$ patterns.
Restrict specification sources: Only consume OpenAPI specifications from trusted internal sources. Avoid automatic code generation from external or third-party APIs until this patch is applied.
Isolate generated code from production: Do not deploy generated PHP models to production environments unless the specification source has been verified and reviewed.
Manual escaping (temporary): If regeneration is not possible, manually inspect and edit generated files to escape any $ characters in double-quoted string literals (replace $ with \$).

Remediation

Upgrade Kiota to 1.29.1, 1.32.4, or later.

Regenerate/refresh existing generated clients as a precaution:

Refreshing generated clients ensures previously generated vulnerable code is replaced with hardened output.

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
.NETNuGet	`Microsoft.OpenApi.Kiota`	≥ 1.30.0&&< 1.32.4	1.32.4`dotnet add package Microsoft.OpenApi.Kiota --version 1.32.4`
.NETNuGet	`Microsoft.OpenApi.Kiota.Builder`	≥ 1.30.0&&< 1.32.4	1.32.4`dotnet add package Microsoft.OpenApi.Kiota.Builder --version 1.32.4`
.NETNuGet	`Microsoft.OpenApi.Kiota`	all versions	1.29.1`dotnet add package Microsoft.OpenApi.Kiota --version 1.29.1`
.NETNuGet	`Microsoft.OpenApi.Kiota.Builder`	all versions	1.29.1`dotnet add package Microsoft.OpenApi.Kiota.Builder --version 1.29.1`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Microsoft.OpenApi.Kiota, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Microsoft.OpenApi.Kiota to 1.32.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59859 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Frequently Asked Questions

# Impact The Kiota PHP code generator is vulnerable to a code generation literal injection attack. The generator embeds string values from OpenAPI fields (e.g. `description`, default values, and property names) directly into PHP double-quoted string literals without properly escaping the `$` character. Since PHP evaluates string interpolation expressions like `"${expr}"`, `"$var"`, and `"{$obj->prop}"` within double-quoted strings at runtime, an attacker who controls an OpenAPI specification file can inject arbitrary PHP code into generated model and request-builder classes. # Who is impacte

O3 Security · Impact-Aware SCA

Is CVE-2026-59859 in your dependencies?

Find it across NuGet, including transitive dependencies.

Scan my dependencies How O3 SCA works