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Meridian: Multiple defense-in-depth gaps (collection/depth caps, telemetry, retry, fan-out)

High severity GitHub Reviewed Published Apr 16, 2026 in UmutKorkmaz/meridian • Updated Apr 16, 2026

Package

nuget Meridian.Mapping (NuGet)

Affected versions

>= 2.0.0, < 2.1.1

Patched versions

2.1.1
nuget Meridian.Mediator (NuGet)
>= 2.0.0, < 2.1.1
2.1.1

Description

Summary

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

# Severity CWE Finding Fix
1 HIGH CWE-770 MappingEngine.TryMapCollectionOntoExisting enumerated the source without enforcing DefaultMaxCollectionItems. Reachable via Mapper.Map<TSrc,TDst>(src, dst) and any .ForMember(..., o => o.UseDestinationValue()) on a collection member through a plain Map(src) call. Shared cap enforcement helper between MapCollection and TryMapCollectionOntoExisting.
2 HIGH CWE-674 Collection-item recursion in the existing-destination path did not increment ResolutionContext.Depth, so self-referential collection graphs could reach stack overflow before DefaultMaxDepth fired. Depth increments at every collection-item boundary.
3 MEDIUM CWE-665 ObjectCreator.CreateWithConstructorMapping always invoked the widest public constructor, silently filling unresolved parameters with default(T) and bypassing narrower-ctor invariants. Widest-ctor selection now requires every parameter to be bound via explicit ctor mapping, source-name match, or a C# optional default.
4 MEDIUM CWE-532 Mediator.MarkActivityFailure emitted the full ex.ToString() (stack + inner chain) to the OpenTelemetry exception.stacktrace activity tag by default, leaking context to any shared trace sink. Gated on MediatorTelemetryOptions.RecordExceptionStackTrace — opt-in, default false.
5 MEDIUM CWE-400 RetryBehavior retried every exception type with unbounded MaxRetries; the exponential-backoff delay overflowed TimeSpan at ~30 attempts. No cancellation exclusion. Server-side MaxRetriesCap = 10, MaxBackoff = 5 min, OperationCanceledException short-circuit, recommended RetryPolicy.TransientOnly helper.
6 MEDIUM CWE-400 TaskWhenAllPublisher started every registered handler concurrently with no bound on fan-out. New constructor parameter maxDegreeOfParallelism (default 16; -1 restores legacy unbounded).
7 LOW CWE-209 Public mapping exceptions leaked FullName of source/destination types and concatenated inner exception messages into top-level property-mapping errors. Scrubbed to type Name; inner details only via InnerException chain.
8 LOW CWE-209 Dictionary materialization threw ArgumentException on duplicate keys, echoing the attacker-supplied key's .ToString(). Last-write-wins indexer semantics.
9 LOW CWE-1325 Static mediator handler caches grow monotonically under closed-generic request types. Doc-only mitigation; no code change — consumers must not allow attacker-controlled runtime type materialization to reach Send, Publish, or CreateStream. Documented in docs/security-model.md.

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.

Patches

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

Verified via:

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

References

@UmutKorkmaz UmutKorkmaz published to UmutKorkmaz/meridian Apr 16, 2026
Published to the GitHub Advisory Database Apr 16, 2026
Reviewed Apr 16, 2026
Last updated Apr 16, 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 v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

Weaknesses

Generation of Error Message Containing Sensitive Information

The product generates an error message that includes sensitive information about its environment, users, or associated data. Learn more on MITRE.

Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource. Learn more on MITRE.

Insertion of Sensitive Information into Log File

The product writes sensitive information to a log file. Learn more on MITRE.

Improper Initialization

The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used. Learn more on MITRE.

Uncontrolled Recursion

The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack. Learn more on MITRE.

Allocation of Resources Without Limits or Throttling

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. Learn more on MITRE.

Improperly Controlled Sequential Memory Allocation

The product manages a group of objects or resources and performs a separate memory allocation for each object, but it does not properly limit the total amount of memory that is consumed by all of the combined objects. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-f5v8-v6q3-q4h6

Source code

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