LiveActive security incident?Get immediate response
CVE Record

CVE-2021-43824: Null pointer dereference in envoy

Envoy is an open source edge and service proxy, designed for cloud-native applications. In affected versions a crafted request crashes Envoy when a CONNECT request is sent to JWT filter configured with regex match. This provides a denial of service attack vector. The only workaround is to not use regex in the JWT filter. Users are advised to upgrade.

HighCVSS 7.5Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This flaw can let an unauthenticated network request crash vulnerable Envoy instances in a specific JWT-filter configuration. For businesses, the impact is availability: affected edge or service-proxy traffic could be disrupted until Envoy restarts or capacity shifts.

Executive priority

Treat as high priority for exposed Envoy gateways because the impact is service availability. It is narrower than a broad remote code execution issue, but affected configurations can be crashed remotely.

Technical view

CVE-2021-43824 is a CWE-476 null pointer dereference in Envoy. A crafted CONNECT request can crash Envoy when the JWT filter is configured with regex match. Affected ranges include 1.21.0 before 1.21.1, 1.20.0 before 1.20.2, 1.19.0 before 1.19.3, and versions before 1.18.6.

Likely exposure

Exposure is most likely where Envoy runs as an edge or service proxy, uses the JWT filter with regex matching, and allows CONNECT requests to reach affected listeners or routes.

Exploitation context

The source bundle describes a denial-of-service vector with network attack characteristics and no authentication required. It does not cite CISA KEV listing or confirmed active exploitation.

Researcher notes

The key exposure condition is configuration-dependent: JWT filter plus regex match handling CONNECT requests. Evidence provided supports denial of service only; it does not support confidentiality impact, integrity impact, or active exploitation claims.

Mitigation direction

  • Upgrade Envoy beyond the affected vendor-listed version ranges.
  • If immediate upgrade is not possible, stop using regex in the JWT filter.
  • Review vendor advisory before changing production proxy behavior.
  • Prioritize internet-facing or shared multi-tenant Envoy deployments first.

Validation and detection

  • Inventory Envoy versions across gateways, sidecars, and service-proxy deployments.
  • Review Envoy configs for JWT filters using regex match.
  • Confirm whether CONNECT requests can reach affected listeners or routes.
  • Check monitoring for unexplained Envoy crashes or restart loops.
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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-476: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-43824 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

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

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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2021-43824Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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>= 1.20.0, < 1.20.2, >= 1.19.0, < 1.19.3, < 1.18.6, >= 1.21.0, < 1.21.1Listed
Weakness

CWE details

CWE-476

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

CWE-476 · source CWE mapping

NULL Pointer Dereference

NULL Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs