Answer in brief
CVE-2021-47555 records a High severity (CVSS 7.8) vulnerability in net: vlan: fix underflow for the real_dev refcnt. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | Not reported | Not reported |
| cpe:2.3:o:linux:linux_kernel:5.16:rc1:*:*:*:*:*:* | Not reported | Not reported |
| cpe:2.3:o:linux:linux_kernel:5.16:rc2:*:*:*:*:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=700602b662d7eaa816b1a3cb0abe7a85de358fd4 <5e44178864b38dd70b877985abd7d86fdb95f27d || >=e04a7a84bb77f9cdf4475340fe931389bc72331c <6e800ee43218a56acc93676bbb3d93b74779e555 || >=21032425c36ff85f16e72ca92193a8c401e4acd5 <f7fc72a508cf115c273a7a29350069def1041890 || >=563bcbae3ba233c275c244bfce2efe12938f5363 <01d9cc2dea3fde3bad6d27f464eff463496e2b00 || fca96b3f852a1b369b7b2844ce357cd689879934 || >=5.14.19 <5.15 | 5e44178864b38dd70b877985abd7d86fdb95f27d, 6e800ee43218a56acc93676bbb3d93b74779e555, f7fc72a508cf115c273a7a29350069def1041890, 01d9cc2dea3fde3bad6d27f464eff463496e2b00, 5.15 |
| Linux/Linuxgeneric | >=5.4.160 <5.4.163 || >=5.10.80 <5.10.83 || >=5.15.3 <5.15.6 | 5.4.163, 5.10.83, 5.15.6 |
Published upstream
May 24, 2024
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 5, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 4, 2026
In the Linux kernel, the following vulnerability has been resolved: net: vlan: fix underflow for the real_dev refcnt Inject error before dev_hold(real_dev) in register_vlan_dev(), and execute the following testcase: ip link add dev dummy1 type dummy ip link add name dummy1.100 link dummy1 type vlan id 100 ip link del dev dummy1 When the dummy netdevice is removed, we will get a WARNING as following: ======================================================================= refcount_t: decrement hit 0; leaking memory. WARNING: CPU: 2 PID: 0 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 and an endless loop of: ======================================================================= unregister_netdevice: waiting for dummy1 to become free. Usage count = -1073741824 That is because dev_put(real_dev) in vlan_dev_free() be called without dev_hold(real_dev) in register_vlan_dev(). It makes the refcnt of real_dev underflow. Move the dev_hold(real_dev) to vlan_dev_init() which is the call-back of ndo_init(). That makes dev_hold() and dev_put() for vlan's real_dev symmetrical.
Quoted source text, attributed separately from HOL analysis.
Answer in brief
CVE-2021-47555 records a High severity (CVSS 7.8) vulnerability in net: vlan: fix underflow for the real_dev refcnt. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | Not reported | Not reported |
| cpe:2.3:o:linux:linux_kernel:5.16:rc1:*:*:*:*:*:* | Not reported | Not reported |
| cpe:2.3:o:linux:linux_kernel:5.16:rc2:*:*:*:*:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=700602b662d7eaa816b1a3cb0abe7a85de358fd4 <5e44178864b38dd70b877985abd7d86fdb95f27d || >=e04a7a84bb77f9cdf4475340fe931389bc72331c <6e800ee43218a56acc93676bbb3d93b74779e555 || >=21032425c36ff85f16e72ca92193a8c401e4acd5 <f7fc72a508cf115c273a7a29350069def1041890 || >=563bcbae3ba233c275c244bfce2efe12938f5363 <01d9cc2dea3fde3bad6d27f464eff463496e2b00 || fca96b3f852a1b369b7b2844ce357cd689879934 || >=5.14.19 <5.15 | 5e44178864b38dd70b877985abd7d86fdb95f27d, 6e800ee43218a56acc93676bbb3d93b74779e555, f7fc72a508cf115c273a7a29350069def1041890, 01d9cc2dea3fde3bad6d27f464eff463496e2b00, 5.15 |
| Linux/Linuxgeneric | >=5.4.160 <5.4.163 || >=5.10.80 <5.10.83 || >=5.15.3 <5.15.6 | 5.4.163, 5.10.83, 5.15.6 |
Published upstream
May 24, 2024
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 5, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 4, 2026
In the Linux kernel, the following vulnerability has been resolved: net: vlan: fix underflow for the real_dev refcnt Inject error before dev_hold(real_dev) in register_vlan_dev(), and execute the following testcase: ip link add dev dummy1 type dummy ip link add name dummy1.100 link dummy1 type vlan id 100 ip link del dev dummy1 When the dummy netdevice is removed, we will get a WARNING as following: ======================================================================= refcount_t: decrement hit 0; leaking memory. WARNING: CPU: 2 PID: 0 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 and an endless loop of: ======================================================================= unregister_netdevice: waiting for dummy1 to become free. Usage count = -1073741824 That is because dev_put(real_dev) in vlan_dev_free() be called without dev_hold(real_dev) in register_vlan_dev(). It makes the refcnt of real_dev underflow. Move the dev_hold(real_dev) to vlan_dev_init() which is the call-back of ndo_init(). That makes dev_hold() and dev_put() for vlan's real_dev symmetrical.
Quoted source text, attributed separately from HOL analysis.