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CVE Record

CVE-2021-36154: HTTP2ToRawGRPCServerCodec in gRPC Swift 1.1.1 and earlier allows remote attackers to deny service via the d...

HTTP2ToRawGRPCServerCodec in gRPC Swift 1.1.1 and earlier allows remote attackers to deny service via the delivery of many small messages within a single HTTP/2 frame, leading to Uncontrolled Recursion and stack consumption.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This vulnerability can let a remote sender crash or exhaust a vulnerable gRPC Swift server by triggering excessive stack use. The known impact is denial of service, not data theft or code execution. Business urgency depends on whether affected Swift gRPC services are internet-facing or support critical operations.

Executive priority

Address this as an availability risk for Swift-based gRPC services. It is most urgent where vulnerable services are externally reachable or operationally critical. Lack of active-exploitation evidence lowers urgency compared with KEV-listed flaws, but unauthenticated remote denial of service can still disrupt business operations.

Technical view

HTTP2ToRawGRPCServerCodec in gRPC Swift 1.1.1 and earlier can recurse uncontrollably when processing many small messages delivered inside one HTTP/2 frame. The result is stack consumption and service denial. The provided sources do not include CVSS, CWE, or a named fixed version.

Likely exposure

Exposure is most likely in Swift services using gRPC Swift 1.1.1 or earlier with reachable gRPC-over-HTTP/2 server endpoints. Internal-only services still matter if they support critical workflows or are reachable from less trusted network segments.

Exploitation context

The CVE describes remote denial of service conditions. The bundle marks CISA KEV as false and provides no evidence of active exploitation. Treat exploit maturity as unconfirmed from the supplied sources.

Researcher notes

The strongest facts are the vulnerable component, affected version boundary, and denial-of-service mechanism. Severity scoring, CWE mapping, and fixed-version details are absent from the supplied bundle, so remediation should be anchored to the GitHub advisory and release history rather than inferred.

Mitigation direction

  • Inventory services using gRPC Swift and identify versions at or below 1.1.1.
  • Review the GitHub advisory and release notes for vendor-confirmed upgrade guidance.
  • Prioritize remediation for internet-facing or business-critical gRPC services.
  • Apply compensating controls to limit untrusted HTTP/2 access where upgrade timing is constrained.
  • Monitor affected services for crashes, stack exhaustion, or repeated availability faults.

Validation and detection

  • Check dependency manifests and lockfiles for grpc-swift versions.
  • Map which affected services expose gRPC-over-HTTP/2 endpoints.
  • Confirm whether exposed endpoints are internet-facing, partner-facing, or internal-only.
  • Review crash logs and service telemetry for unexplained stack or recursion failures.
  • Document the remediated version and supporting vendor reference.
Prepared
Confidence
medium
Sources
5

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2021-36154 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
4Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.