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CVE Record

CVE-2021-43825: Use-after-free in Envoy

Envoy is an open source edge and service proxy, designed for cloud-native applications. Sending a locally generated response must stop further processing of request or response data. Envoy tracks the amount of buffered request and response data and aborts the request if the amount of buffered data is over the limit by sending 413 or 500 responses. However when the buffer overflows while response is processed by the filter chain the operation may not be aborted correctly and result in accessing a freed memory block. If this happens Envoy will crash resulting in a denial of service.

MediumCVSS 6.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Envoy can crash when handling certain oversized buffered response data through its filter chain. The main business impact is denial of service for applications relying on affected Envoy proxies at the edge, ingress, egress, or service-mesh layer.

Executive priority

Treat as a service availability issue. Patch internet-facing and high-traffic Envoy deployments promptly, especially where proxy crashes would disrupt customer access or internal service communication.

Technical view

CVE-2021-43825 is a CWE-416 use-after-free in Envoy. A locally generated 413 or 500 response should stop further processing, but response-path buffer overflow handling may continue and access freed memory, causing process crash.

Likely exposure

Organizations are exposed if they run Envoy versions below 1.18.6, 1.19.0 to below 1.19.3, 1.20.0 to below 1.20.2, or 1.21.0 to below 1.21.1.

Exploitation context

The source bundle does not show CISA KEV listing or cited evidence of active exploitation. The documented impact is crash-based denial of service, not confirmed data theft or remote code execution.

Researcher notes

Evidence supports a response-filter-chain buffer handling flaw that can reach freed memory after local error response generation. Sources do not provide exploit status, broad product derivatives, or configuration-specific prerequisites beyond affected Envoy versions.

Mitigation direction

  • Upgrade Envoy to a version outside the listed affected ranges.
  • Prioritize public edge, ingress, egress, and service-mesh proxy deployments.
  • Check the Envoy advisory for vendor-specific upgrade guidance.
  • Monitor proxy crash loops and abnormal 413 or 500 response patterns.

Validation and detection

  • Inventory all Envoy binaries and container images in production and staging.
  • Compare deployed versions against the affected version ranges.
  • Review edge and service-mesh proxies before lower-risk internal deployments.
  • Confirm upgraded instances restart cleanly and remain stable under normal traffic.
Prepared
Confidence
high
Sources
4

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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cwe · low confidence lookup

CWE-416: Exact CWE lookup

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cve · low confidence lookup

CVE-2021-43825 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:L

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.

1CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
6.1CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:L2.82.7Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.1Medium
CVSS 3.1 vector shape for CVE-2021-43825Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:L

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
envoyproxyenvoy< 1.18.6, >= 1.19.0, < 1.19.3, >= 1.20.0, < 1.20.2, >= 1.21.0, < 1.21.1Listed
Weakness

CWE details

CWE-416

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

CWE-416 · source CWE mapping

Use After Free

Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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