Security readout for executives and security teams
Plain-English summary
CVE-2021-4090 is a Linux kernel NFSD memory corruption flaw. A local user could trigger an out-of-bounds write in NFSv4 bitmap decoding, potentially affecting confidentiality and integrity. The bundle identifies kernel 5.16 rc2 and does not provide CVSS scoring or confirmed exploitation.
Executive priority
Treat this as a targeted kernel maintenance issue, not an internet-wide emergency based on the provided evidence. Prioritize NFS-capable Linux servers and vendor-managed appliances, especially where local users or shared shell access exist.
Technical view
The flaw is a CWE-787 out-of-bounds write in fs/nfsd/nfs4xdr.c, nfsd4_decode_bitmap4. Missing sanity checking may allow a write beyond bmval[bmlen-1]. Sources describe a local attacker with user privileges and possible out-of-bounds memory access.
Likely exposure
Exposure appears most relevant to Linux systems using the affected NFSD code path, with kernel 5.16 rc2 specifically named. NetApp and Siemens advisories are referenced, so appliance exposure should be checked against those vendor advisories rather than assumed.
Exploitation context
The provided bundle does not show CISA KEV listing, public exploitation, or weaponized exploit evidence. The stated attacker position is local user privilege, not unauthenticated remote access.
Researcher notes
Evidence is limited to the CVE description and linked advisories. The kernel mailing-list reference likely identifies the upstream fix context, but the bundle does not include full patch details, exploitability analysis, or affected downstream versions beyond kernel 5.16 rc2.
Mitigation direction
- Check the Linux kernel and vendor advisories for fixed versions.
- Prioritize systems running NFSD or NFS server services.
- Review NetApp and Siemens advisories for product-specific guidance.
- Restrict local user access on exposed Linux servers where feasible.
- Track distribution security notices for backported kernel fixes.
Validation and detection
- Inventory Linux kernel versions and identify any 5.16 rc2 systems.
- Confirm whether NFSD/NFS server functionality is enabled.
- Review distribution package changelogs for CVE-2021-4090 fixes.
- Check NetApp and Siemens advisory applicability for managed appliances.
- Document compensating controls if immediate patching is not possible.
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-2021-4090 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.
- 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://bugzilla.redhat.com/show_bug.cgi?id=2025101CVE reference, redhat
- https://lore.kernel.org/linux-nfs/163692036074.16710.5678362976688977923.stgit%40klimt.1015granger.net/CVE reference, redhat
- https://security.netapp.com/advisory/ntap-20220318-0010/CVE reference, redhat
- https://cert-portal.siemens.com/productcert/html/ssa-265688.htmlCVE reference, siemens-SADP
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.