Security readout for executives and security teams
Plain-English summary
CVE-2021-47126 is a Linux kernel flaw in IPv6 routing cleanup code. A local low-privileged user could potentially trigger a kernel out-of-bounds read leading to denial of service. The available sources do not show data theft, integrity impact, or active exploitation.
Executive priority
Treat as a moderate patching item. It is availability-focused and local, but kernel denial-of-service issues matter on shared infrastructure. Prioritize shared hosts, production Linux fleets, and container platforms before isolated endpoints.
Technical view
The flaw is a CWE-125 slab out-of-bounds read in fib6_nh_flush_exceptions via fib6_nh_get_excptn_bucket in net/ipv6/route.c. It was found by syzbot/KASAN and resolved in Linux stable commits. CVSS 3.1 is 5.5: local, low complexity, low privileges, no user interaction, availability high.
Likely exposure
Exposure is mainly Linux systems running affected kernel versions, especially multi-user hosts or environments allowing untrusted local workloads. This is not described as remotely exploitable in the provided sources.
Exploitation context
The CVE is not in KEV, and the source bundle provides no evidence of active exploitation. The report comes from syzbot crash testing, with impact characterized as local denial of service rather than confidentiality or integrity compromise.
Researcher notes
Key evidence is the KASAN slab-out-of-bounds read in IPv6 route exception flushing. The affected-version data in the bundle is limited and should be reconciled against distro advisories and the referenced stable commits before declaring systems fixed.
Mitigation direction
- Update to a vendor kernel containing the referenced stable fixes.
- Check Linux distribution advisories for backported fixed package versions.
- Prioritize hosts with untrusted local users or workloads.
- If patching is delayed, reduce access for untrusted local accounts.
- Track vendor guidance; no separate mitigation is named in sources.
Validation and detection
- Inventory Linux kernel versions across servers and images.
- Compare deployed kernels with vendor fixed versions or backport notices.
- Confirm security update installation and reboot into the fixed kernel.
- Review vulnerability scanner findings for CVE-2021-47126 accuracy.
- Check whether affected systems permit untrusted local execution.
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-125: 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-2021-47126 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
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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.
SSVC decision data
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:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6CISA-ADPVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://git.kernel.org/stable/c/7ba7fa78a92dc410b6f93ed73075ab669c3a0b59CVE reference, Linux
- https://git.kernel.org/stable/c/09870235827451409ff546b073d754a19fd17e2eCVE reference, Linux
- https://git.kernel.org/stable/c/0a462e25ef0f7ab305081a08d435bbd1f13c0a94CVE reference, Linux
- https://git.kernel.org/stable/c/821bbf79fe46a8b1d18aa456e8ed0a3c208c3754CVE reference, Linux
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 Read
Out-of-bounds Read represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.