GHSA-F5V8-V6Q3-Q4H6

Meridian v2.1.0 (Meridian.Mapping and Meridian.Mediator) shipped with nine defense-in-depth gaps reachable through its public APIs. Two are HIGH severity, the advertised DefaultMaxCollectionItems and DefaultMaxDepth safety caps are silently bypassed on the IMapper.Map(source, destination) overload and anywhere .UseDestinationValue() is configured on a collection-typed property. Four are MEDIUM (constructor invariant bypass, OpenTelemetry stack-trace info disclosure, retry amplification, notification fan-out amplification). Three are LOW (exception message disclosure, dictionary duplicate-key echo, static mediator cache growth under closed-generic types).

All nine are patched in v2.1.1. Upgrade is a drop-in NuGet bump; see the v2.1.1 CHANGELOG for the four behavioural changes (constructor selection, OTel default, publisher fan-out cap, retry caps).

Severity Matrix

Exploitation

Finding 1 / 2 (headline): A consumer that maps user-supplied collection payloads onto an existing destination list via mapper.Map(userCollection, existingList), a documented and commonly used AutoMapper-style idiom, processes the full attacker-supplied collection with no size cap and no depth cap. An attacker sending a single request with a large (or self-referential) collection payload can block the worker thread for seconds and exhaust the managed heap or the call stack. Equivalent exposure through .UseDestinationValue() on a collection-typed destination member, reachable via a plain Map(src) call whose destination type default-initializes that member.

Finding 3: A destination type with multiple public constructors that differ only in their parameter-binding invariants (e.g., new UserAccount(string name, Email email) enforcing a non-default Email) could be instantiated with the narrower ctor's invariants silently bypassed if any source field was absent, the widest ctor was always picked, with unbound parameters replaced by default(T).

Findings 4 / 5 / 6: Amplification / information-disclosure vectors described in the matrix above. Each requires moderate integration context (telemetry sink trust, handler count, retry policy) to weaponize, but each is reachable through public APIs without authentication.

Workarounds

Users who cannot upgrade immediately may:

1. Avoid mapper.Map(src, dst) and .UseDestinationValue() on collection-typed destination members.
2. Wrap input collection deserialization with an explicit size limit before handing the payload to Meridian.
3. Register TaskWhenAllPublisher with maxDegreeOfParallelism ≤ 16 manually (v2.1.1+ only).
4. Disable OpenTelemetry exception.stacktrace tag emission at the trace exporter level if your trace sink is less trusted than your application.

These are defense-in-depth; the only complete mitigation is upgrading to 2.1.1.

Supported Versions

As of this advisory the supported security branch is 2.1.x. The 2.0.x line (published 2026-04-15) is not receiving the Phase 1 safety-defaults infrastructure needed to carry the HIGH-severity fixes, so 2.0.x is deprecated in favor of 2.1.x. See SECURITY.md for the updated supported-versions table.

Credits

• UmutKorkmaz (reporter and maintainer)

References

• v2.1.1 CHANGELOG section: https://github.com/UmutKorkmaz/meridian/blob/main/CHANGELOG.md#211---2026-04-16
• docs/security-model.md threat model: https://github.com/UmutKorkmaz/meridian/blob/main/docs/security-model.md
• SECURITY.md disclosure policy: https://github.com/UmutKorkmaz/meridian/blob/main/SECURITY.md
• AutoMapper CVE-2026-32933 (motivating precedent for Meridian's safety-defaults)

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

GHSA-F5V8-V6Q3-Q4H6 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.1.1); upgrading removes the vulnerable code path.

Kodem intelligence

• Meridian.Mapping 2.1.1 (published 2026-04-16)
• Meridian.Mediator 2.1.1 (published 2026-04-16)

Verified via:

• GitHub Release assets at https://github.com/UmutKorkmaz/meridian/releases/tag/v2.1.1
• Sigstore attestation (actions/attest-build-provenance@v2 → gh attestation verify green on both .nupkg from the GitHub Release)
• NuGet.org indexed both packages within the release workflow run

1. What is GHSA-F5V8-V6Q3-Q4H6? GHSA-F5V8-V6Q3-Q4H6 is a high-severity uncontrolled resource consumption vulnerability in Meridian.Mapping (nuget), affecting versions >= 2.0.0, < 2.1.1. It is fixed in 2.1.1. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is GHSA-F5V8-V6Q3-Q4H6? GHSA-F5V8-V6Q3-Q4H6 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by GHSA-F5V8-V6Q3-Q4H6?
   • Meridian.Mapping (nuget) (versions >= 2.0.0, < 2.1.1)
   • Meridian.Mediator (nuget) (versions >= 2.0.0, < 2.1.1)
4. Is there a fix for GHSA-F5V8-V6Q3-Q4H6? Yes. GHSA-F5V8-V6Q3-Q4H6 is fixed in 2.1.1. Upgrade to this version or later.
5. Is GHSA-F5V8-V6Q3-Q4H6 exploitable, and should I be worried? Whether GHSA-F5V8-V6Q3-Q4H6 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether GHSA-F5V8-V6Q3-Q4H6 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix GHSA-F5V8-V6Q3-Q4H6?
   • Upgrade Meridian.Mapping to 2.1.1 or later
   • Upgrade Meridian.Mediator to 2.1.1 or later