Security readout for executives and security teams
Plain-English summary
CVE-2021-47236 is a Linux kernel bug in the USB CDC EEM networking driver. In a transmit error path, a network buffer may not be freed, causing a memory leak. The sources do not provide a CVSS score, confirmed attacks, or distribution-specific impact.
Executive priority
Treat as a routine kernel maintenance issue unless critical systems rely on USB CDC EEM networking. There is no cited active exploitation, no CVSS score, and no evidence of broad remote exposure in the provided sources.
Technical view
The issue is in eem_tx_fixup() for cdc_eem. If skb_copy_expand() fails, it returns NULL before the original skb is freed, leaving usbnet_start_xmit() unable to release it. Kernel stable commits free the original skb before returning on failure.
Likely exposure
Exposure appears limited to Linux systems using the cdc_eem USB networking transmit path. The provided sources list affected Linux kernel versions and stable commits, but do not identify affected distributions, default configurations, or required local conditions.
Exploitation context
The source bundle shows KEV is false and provides no evidence of active exploitation or public weaponization. Based on the description, practical impact is most likely resource exhaustion through repeated transmit failure conditions, but exploitability is not established.
Researcher notes
The key defect is a missed skb free on an allocation failure path in eem_tx_fixup(). Validate reachability through cdc_eem transmit handling and kernel version lineage. The record is sparse, so avoid assuming distribution impact without vendor confirmation.
Mitigation direction
- Apply vendor kernel updates that include the referenced stable fixes.
- Confirm distribution kernels have backported the cdc_eem skb leak fix.
- Reduce exposure to untrusted USB networking devices where operationally feasible.
- Check vendor guidance if running custom or long-term kernel builds.
Validation and detection
- Inventory Linux kernel versions across affected assets.
- Check whether cdc_eem or USB networking support is enabled or loaded.
- Compare deployed kernels with vendor advisories or referenced stable commits.
- Review kernel logs for cdc_eem or usbnet use on exposed systems.
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
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CVE-2021-47236 mapping review
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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.
SSVC decision data
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/f12554b0ff639e74612cc01b3b4a049e098d2d65CVE reference, Linux
- https://git.kernel.org/stable/c/14184ec5c958b589ba934da7363a2877879204dfCVE reference, Linux
- https://git.kernel.org/stable/c/1bcacd6088d61c0ac6a990d87975600a81f3247eCVE reference, Linux
- https://git.kernel.org/stable/c/f4e6a7f19c82f39b1803e91c54718f0d7143767dCVE reference, Linux
- https://git.kernel.org/stable/c/81de2ed06df8b5451e050fe6a318af3263dbff3fCVE reference, Linux
- https://git.kernel.org/stable/c/05b2b9f7d24b5663d9b47427fe1555bdafd3ea02CVE reference, Linux
- https://git.kernel.org/stable/c/b4f7a9fc9d094c0c4a66f2ad7c37b1dbe9e78f88CVE reference, Linux
- https://git.kernel.org/stable/c/c3b26fdf1b32f91c7a3bc743384b4a298ab53ad7CVE 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.