Security readout for executives and security teams
Plain-English summary
CVE-2021-21257 is a memory corruption flaw in Contiki-NG, an IoT operating system. A network packet reaching affected RPL routing code can trigger out-of-bounds writes. The practical impact is integrity risk and some availability risk for devices running Contiki-NG before 4.6.
Executive priority
Treat as a high-priority IoT platform remediation item where Contiki-NG is used. Urgency is strongest for devices exposed to reachable or injectable network traffic. No active exploitation is evidenced in the provided sources.
Technical view
RPL-Classic and RPL-Lite before Contiki-NG 4.6 fail to validate an address pointer derived from the source routing header CMPR field. The vulnerable rpl_ext_header_srh_update function can use that pointer as a memcpy destination, causing out-of-bounds writes.
Likely exposure
Exposure is limited to products, firmware, or projects using Contiki-NG versions before 4.6 with RPL-Classic or RPL-Lite enabled. The source bundle does not identify downstream affected devices or vendors.
Exploitation context
The CVSS vector indicates network attack, low complexity, no privileges, and no user interaction. The bundle does not show CISA KEV listing or any cited evidence of active exploitation.
Researcher notes
The vulnerability maps to CWE-787 and affects rpl_ext_header_srh_update in both RPL-Lite and RPL-Classic. The root issue is unvalidated CMPR-derived pointer arithmetic before memcpy. Evidence is strong for upstream Contiki-NG, but downstream product impact is not documented here.
Mitigation direction
- Upgrade affected Contiki-NG deployments to version 4.6 or later.
- Apply the vendor patch out-of-band if immediate upgrade is not feasible.
- Review Contiki-NG advisory GHSA-mvc7-9p4q-c5cm for vendor guidance.
- Prioritize devices where RPL packet processing is reachable from untrusted networks.
Validation and detection
- Inventory firmware and build manifests for Contiki-NG versions before 4.6.
- Confirm whether RPL-Classic or RPL-Lite is compiled or enabled.
- Check whether the vulnerable rpl-ext-header.c modules are present.
- Verify remediation by confirming version 4.6 or the referenced patch is applied.
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-787: 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-2021-21257 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
- High
- CVSS
- 8.2 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L3.94.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.2HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/contiki-ng/contiki-ng/security/advisories/GHSA-mvc7-9p4q-c5cmCVE reference · x_refsource_CONFIRM
- https://github.com/contiki-ng/contiki-ng/pull/1431CVE reference · x_refsource_MISC
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.
Out-of-bounds Write
Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.