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Microsoft Kiota: Arbitrary file write + code-injection via x-ms-kiota-info clientClassName and clientNamespaceName

High severity GitHub Reviewed Published Jul 3, 2026 in microsoft/kiota • Updated Jul 24, 2026

Package

nuget Microsoft.OpenApi.Kiota (NuGet)

Affected versions

< 1.32.5

Patched versions

1.32.5
nuget Microsoft.OpenApi.Kiota.Builder (NuGet)
< 1.32.5
1.32.5

Description

Summary

Microsoft Kiota emitted the x-ms-kiota-info extension's clientClassName or clientNamespaceName value
raw, with no identifier or path sanitization, as both the generated client's class/namespace name
and part of the generated output path. When kiota generate is run without -c/--class-name — the
zero-config workflow that x-ms-kiota-info is explicitly designed for (the API provider supplies the names in
the description so consumers don't have to) — an attacker who controls or tampers with the OpenAPI description
could therefore:

  • (CWE-22) write the generated source file to a path outside the -o output directory — e.g.
    clientClassName: "/var/www/html/shell"; and
  • (CWE-94) inject arbitrary text into the generated class/namespace declaration, corrupting the generated
    client.

Confirmed on Kiota 1.32.4 (the self-contained linux-x64 release binary), i.e. after the earlier
writer-sink hardening — that fix escaped property/enum/default/serialization sinks but never sanitized the
provider-supplied clientClassName / clientNamespaceName.

Details

clientClassName reached two unsanitized sinks (observed in the generated C#; the same raw emission occurred
for Java, Go, TypeScript, Python, and PHP):

# output FILENAME (CWE-22): clientClassName flows into the file path
clientClassName: "/abs/path/PWNED"   ->   /abs/path/PWNED.cs   (written outside -o)

# class declaration (CWE-94): clientClassName flows verbatim into the type declaration
clientClassName: 'Pwn { } public class INJECTED { } public partial class RealClient'
   ->  public partial class Pwn { } public class INJECTED { } public partial class RealClient : ... { }

clientNamespaceName reached the analogous namespace/path sinks.

Impact

A developer or CI host generating a client from an attacker-controlled or compromised OpenAPI description
(without -c) could create/overwrite a generated source file at an attacker-influenced path and emit
attacker-controlled text into the generated client.

This does not reach clean remote code execution: because clientClassName is reused verbatim at multiple
sites (the class name and the constructor name), injected code cannot be made to compile — it breaks the
build. So the code-injection vector is a generation/build-corruption (integrity/DoS), and the high-severity
primitive is the file write. CWE-22 / CWE-94.

Patches

Fixed in 1.32.5 (microsoft/kiota#7884). clientClassName and
clientNamespaceName sourced from x-ms-kiota-info are now sanitized before use:
GenerationConfiguration.SanitizeClientClassName strips any character outside [A-Za-z0-9_] and any invalid
leading character (falling back to ApiClient), and SanitizeClientNamespaceName restricts to
[A-Za-z0-9._-], collapses consecutive dots, strips invalid leading characters (falling back to ApiSdk).
This removes path separators, drive/colon, .., quotes, and braces, so the values can no longer influence
the output path or inject into the declaration.

Remediation

Upgrade to Kiota 1.32.5 or later and regenerate affected clients.

References

@jingjingjia-ms jingjingjia-ms published to microsoft/kiota Jul 3, 2026
Published by the National Vulnerability Database Jul 16, 2026
Published to the GitHub Advisory Database Jul 24, 2026
Reviewed Jul 24, 2026
Last updated Jul 24, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction Active
Vulnerable System Impact Metrics
Confidentiality None
Integrity High
Availability Low
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(69th percentile)

Weaknesses

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Learn more on MITRE.

Improper Control of Generation of Code ('Code Injection')

The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. Learn more on MITRE.

CVE ID

CVE-2026-59866

GHSA ID

GHSA-4vv7-jj25-4gh6

Source code

Credits

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