This CVE exploits a fundamental ordering failure in request validation. The openapi3filter library is designed to validate incoming requests against OpenAPI schemas before processing—but its sliceMapToSlice function allocates heap memory based on attacker-supplied array indexes BEFORE maxItems constraints are checked. An attacker can send a query string like param[items][50000000]=x to force allocation of a 50-million-entry slice in a single request, consuming gigabytes of memory before the server can reject it. This is a classic allocation-then-validate bug that has appeared across ecosystems in XML parsers, marshaling libraries, and query string handlers—except here it lives in a security filter that developers explicitly trust to enforce schema constraints. The vulnerable code path triggers through deepObject serialization, a standards-compliant OpenAPI 3.0 encoding for nested objects in query strings, making this attack viable against any API using this parameter style. The 0.142.0 patch likely validates bounds before allocation, but verify whether this restores the complete constraint-checking pipeline or just patches the most obvious gap. Other schema constraints like maxLength, pattern matching, and type coercion may still execute post-allocation on this same path—assume the fix is incomplete until confirmed. Check whether any downstream services disabled their own validation after deploying this gateway; they may now be exposed. If you maintain services using kin-openapi below 0.142.0 and expose deepObject query parameters, treat this as an immediate priority. Monitor for anomalous memory pressure correlated with request patterns, and audit your OpenAPI specs for maxItems declarations on array parameters in deepObject-serialized endpoints.
CVE-2026-77354
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedkin-openapi is a Go project for handling OpenAPI files. From 0.124.0 until 0.142.0, openapi3filter.sliceMapToSlice in openapi3filter/req_resp_decoder.go converts attacker-controlled sparse indexes from a deepObject query parameter into a dense slice by allocating entries from zero through the largest supplied index, after which buildResObj creates another slice of the same length. This allocation occurs before schema validation, so maxItems does not prevent it. An unauthenticated client can send a small query such as param[items][50000000]=x to an endpoint whose deepObject schema contains an array, forcing multi-gigabyte heap allocation and causing an OOM kill or restart loop. Other request-body encodings and styled parameters that do not produce bracketed integer indexes are not affected. This issue is fixed in version 0.142.0.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisA single request can consume unbounded CPU, memory, or connections, so a modest amount of malicious traffic exhausts the service. The result is denial of service for everyone else. Remediation is enforcing limits, quotas, and timeouts on what any one request can use.
General guidance for the uncontrolled resource consumption class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- Authentication
- X
- User interaction
- None
- Scope
- X
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedkin-openapi v0.142.0
- Update the go.mod file to require kin-openapi v0.142.0 or later (e.g., replace the existing kin-openapi requirement with `github.com/getkin/kin-openapi v0.142.0`)
- Run `go mod tidy` to update the dependency lock file
- Rebuild and test the application to ensure the upgrade does not introduce regressions
- If using Go modules, verify with `go list -m all` that the correct version is resolved
Generated from the published advisory — verify against the referenced sources before acting.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-77354 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesThis CVE exploits a fundamental ordering failure in request validation. The openapi3filter library is designed to validate incoming requests against OpenAPI schemas before processing—but its sliceMapToSlice function allocates heap memory based on attacker-supplied array indexes BEFORE maxItems constraints are checked. An attacker can send a query string like `param[items][50000000]=x` to force allocation of a 50-million-entry slice in a single request, consuming gigabytes of memory before the server can reject it. This is a classic allocation-then-validate bug that has appeared across ecosystems in XML parsers, marshaling libraries, and query string handlers—except here it lives in a security filter that developers explicitly trust to enforce schema constraints. The vulnerable code path triggers through deepObject serialization, a standards-compliant OpenAPI 3.0 encoding for nested objects in query strings, making this attack viable against any API using this parameter style. The 0.142.0 patch likely validates bounds before allocation, but verify whether this restores the complete constraint-checking pipeline or just patches the most obvious gap. Other schema constraints like maxLength, pattern matching, and type coercion may still execute post-allocation on this same path—assume the fix is incomplete until confirmed. Check whether any downstream services disabled their own validation after deploying this gateway; they may now be exposed. If you maintain services using kin-openapi below 0.142.0 and expose deepObject query parameters, treat this as an immediate priority. Monitor for anomalous memory pressure correlated with request patterns, and audit your OpenAPI specs for maxItems declarations on array parameters in deepObject-serialized endpoints.
Practitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-77354 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data