Fix CVE-2026-40021: upgrade log4net to 3.3.0 in examples/WireMock.Net.Service/packages.config

[Copilot]

log4net < 3.3.0 fails to sanitize XML 1.0 forbidden characters in XmlLayout/XmlLayoutSchemaLog4J, allowing an attacker to silently suppress log events by injecting forbidden characters into MDC fields or the identity field (CVE-2026-40021 / GHSA-4f7c-pmjv-c25w).

Changes

• examples/WireMock.Net.Service/packages.config — bumped log4net from 2.0.15 → 3.3.0 to align with the PackageReference already declared at 3.3.0 in the .csproj.

Reachability

The vulnerable APIs (XmlLayout, XmlLayoutSchemaLog4J, MDC properties) are not used anywhere in the codebase. The service uses only PatternLayout. This update resolves the scanner alert but does not patch an actively exploitable path.

Original prompt

---

This section details the Dependabot vulnerability alert you should resolve

<alert_title>Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescaped XML 1.0 forbidden characters</alert_title>
<alert_description>Apache Log4net's XmlLayout https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list and XmlLayoutSchemaLog4J https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list , in versions before 3.3.0, fail to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets in MDC property keys and values, as well as the identity field that may carry attacker-influenced data. This causes an exception during serialization and the silent loss of the affected log event.

An attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity.

Users are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue.</alert_description>

moderate
GHSA-4f7c-pmjv-c25w, CVE-2026-40021
log4net
nuget
<vulnerable_versions>= 2.0.15</vulnerable_versions>
<patched_version>3.3.0</patched_version>
<manifest_path>examples/WireMock.Net.Service/packages.config</manifest_path>

https://nvd.nist.gov/vuln/detail/CVE-2026-40021 https://github.com/apache/logging-log4net/pull/280 https://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7 https://logging.apache.org/cyclonedx/vdr.xml https://logging.apache.org/log4net/manual/configuration/layouts.html https://logging.apache.org/security.html#CVE-2026-40021 http://www.openwall.com/lists/oss-security/2026/04/10/11 https://github.com/advisories/GHSA-4f7c-pmjv-c25w

<task_instructions>Resolve this alert by updating the affected package to a non-vulnerable version. Prefer the lowest non-vulnerable version (see the patched_version field above) over the latest to minimize breaking changes. Include a Reachability Assessment section in the PR description. Review the alert_description field to understand which APIs, features, or configurations are affected, then search the codebase for usage of those specific items. If the vulnerable code path is reachable, explain how (which files, APIs, or call sites use the affected functionality) and note that the codebase is actively exposed to this vulnerability. If the vulnerable code path is not reachable, explain why (e.g. the affected API is never called, the vulnerable configuration is not used) and note that the update is primarily to satisfy vulnerability scanners rather than to address an active risk. If the advisory is too vague to determine reachability (e.g. 'improper input validation' with no specific API named), state that reachability could not be determined and explain why. Include a confidence level in the reachability assessment (e.g. high confidence if the advisory names a specific API and you confirmed it is or is not called, low confidence if the usage is indirect and hard to trace). If no patched version is available, check the alert_description field for a Workarounds section — the advisory may describe configuration changes or usage patterns that mitigate the vulnerability without a version update. If a workaround is available, apply it and leave a code comment referencing the advisory identifier explaining it is a temporary mitigation. If neither a patch nor a workaround is available, explain in the PR description why the alert cannot be resolved automatically so a human reviewer can take over. Inspect the repository to determine which package manager is used (e.g. lock files, config files, build scripts) and use that tooling to perform the update — do not edit lock files directly. If the version constraint in the manifest (e.g. package.json, Gemfile, pyproject.toml) caps the version below the fix, update the constraint first. For transitive dependencies, determine whether it is simpler to update the direct dependency that pulls in the vulnerable package or to update the transitive dependency directly, and choose the least disruptive approach. If upgrading to fix the vulnerability forces a major version bump or known breaking changes, review the changelog or release notes, then audit the codebase for usage of affected APIs and fix any breaking changes that are found. If the package manager fails to resolve dependencies (e.g. peer dependency conflicts, incompatible engine constraints), document the error in the PR description rather than attempting increasingly complex workarounds. After updating, check the lock file to confirm the package no longer resolves to a version in the vulnerable range. Keep changes minimal and tightly scoped. Ensure tests, build, type checking, and linting all pass after your chan...