Security readout for executives and security teams
Plain-English summary
CVE-2021-27821 is a cross-site scripting issue in the OpenWrt LuCI web interface in version 19.07 and lower. The public bundle does not provide severity, CVSS, affected CPEs, exploit details, or a named patch. Treat exposure as meaningful where router management interfaces are reachable by untrusted users.
Executive priority
Prioritize identification and access restriction first. Escalate remediation for internet-exposed or broadly reachable management interfaces because router administration sessions can be high-impact, even though severity details are incomplete.
Technical view
The CVE description identifies an XSS vulnerability in OpenWrt LuCI 19.07 and lower. The record does not specify XSS type, affected parameters, authentication requirements, impact scope, or remediation version. KEV status is false in the provided bundle, so active exploitation is not evidenced here.
Likely exposure
Likely exposure is OpenWrt deployments using LuCI 19.07 or lower, especially where the web management interface is reachable from user networks, VPN users, or the internet.
Exploitation context
The provided sources do not show active exploitation, public exploit availability, or KEV listing. XSS risk depends heavily on interface reachability, user interaction, authentication context, and browser session privileges.
Researcher notes
The source bundle is sparse: no CVSS, CWE, affected CPEs, proof of exploitation, vulnerable parameter, or fixed release is provided. Analysis should remain conservative until OpenWrt advisory details are confirmed.
Mitigation direction
- Inventory OpenWrt devices and identify LuCI versions.
- Review OpenWrt advisory and release guidance for supported upgrade paths.
- Restrict LuCI access to trusted administration networks only.
- Disable internet exposure for the LuCI management interface.
- Monitor vendor guidance before asserting a specific patched version.
Validation and detection
- Confirm whether each OpenWrt device runs LuCI 19.07 or lower.
- Check whether LuCI is exposed beyond trusted admin networks.
- Review access logs for unexpected LuCI management activity.
- Verify upgrade status against OpenWrt release documentation.
- Document compensating controls where upgrades are delayed.
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.
CVE-2021-27821 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
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
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.
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- ADP timelineCVE
Previously entered references were removed because they are not applicable to this CVE Record.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2026-07-08T22:21:05.413Z: Previously entered references were removed because they are not applicable to this CVE Record.
Source materials
- CVE List V5 sourceCVE List V5
- https://openwrt.org/advisory/startCVE reference, mitre
- https://openwrt.org/releases/19.07/startCVE reference, mitre
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.