Security readout for executives and security teams
Plain-English summary
CVE-2021-4437 is a low-severity denial-of-service risk in dbartholomae lambda-middleware frameguard versions 1.0.0 through 1.0.4. A crafted input to JSON MIME-type handling may cause inefficient regular-expression processing, reducing availability. The cited fix is upgrading to version 1.1.0.
Executive priority
Handle in normal patch cycles unless the affected component protects business-critical serverless paths or high-volume request handling. The business risk is availability degradation, not data theft or integrity compromise based on the supplied sources.
Technical view
The issue is CWE-1333 inefficient regular expression complexity in packages/json-deserializer/src/JsonDeserializer.ts, affecting the JSON Mime-Type Handler. CVSS 3.1 is 3.5 with adjacent access, low attack complexity, low privileges, no user interaction, and low availability impact. Patch commit f689404d830cbc1edd6a1018d3334ff5f44dc6a6 addresses it.
Likely exposure
Exposure is limited to applications using affected dbartholomae lambda-middleware frameguard versions 1.0.0 through 1.0.4. The CVSS vector indicates adjacent access and prior low privileges, so broad unauthenticated internet exposure is not supported by the supplied evidence.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation. VulDB classifies the issue as problematic and permission-required. Treat it as a targeted availability concern where affected JSON MIME-type processing is reachable by a low-privileged adjacent actor.
Researcher notes
Evidence names the affected file and patch but describes the impacted functionality as unknown. Validate package naming carefully because the source bundle associates frameguard with JSON deserializer code. Do not claim exploit maturity without additional cited evidence.
Mitigation direction
- Upgrade the affected component to version 1.1.0 or later.
- Prioritize services where JSON MIME-type handling is reachable by untrusted users.
- Check vendor release notes and patch commit for any deployment-specific guidance.
- Monitor request latency and error rates after updating.
Validation and detection
- Inventory dependencies for lambda-middleware frameguard versions 1.0.0 through 1.0.4.
- Confirm deployed builds use version 1.1.0 or later.
- Identify services using JSON deserialization through this middleware.
- Review logs for unusual request latency without assuming exploitation.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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-1333: 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 lookupCVE-2021-4437 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Low
- CVSS
- 3.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
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.
CVSS vector scores
1 official scoreWe 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.
CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L2.11.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
3.5LowVector: CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Source materials
- CVE List V5 sourceCVE List V5
- https://vuldb.com/?id.253406CVE reference · vdb-entry
- https://vuldb.com/?ctiid.253406CVE reference · signature, permissions-required
- https://github.com/dbartholomae/lambda-middleware/pull/57CVE reference · issue-tracking
- https://github.com/dbartholomae/lambda-middleware/commit/f689404d830cbc1edd6a1018d3334ff5f44dc6a6CVE reference · patch
- https://github.com/dbartholomae/lambda-middleware/releases/tag/%40lambda-middleware%2Fframeguard_v1.1.0CVE reference · patch
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Inefficient Regular Expression Complexity
Inefficient Regular Expression Complexity represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.