CVE-2026-99282
Description
A flaw was found in the Linux kernel's Traffic Equalizer (sch_teql) network scheduler. This flaw allows an attacker to cause a Denial of Service (DoS) by transmitting network traffic through an affected network interface. During packet transmission, if a subordinate network device or lower queueing discipline drops a packet, the teql driver fails to recognize that the packet buffer was consumed and freed. Consequently, the kernel attempts to access the already freed buffer, resulting in a use-after-free condition and a system crash.
Statement
sch_teql treated every ndo_start_xmit result other than NETDEV_TX_OK as if the skb had not been consumed. A VLAN slave can propagate NET_XMIT_DROP after the lower qdisc has already freed the skb, after which teql_master_xmit writes skb dev and calls __skb_pull on freed memory. This provides a concrete use after free access and can cause a kernel crash. Reallocation of the freed skb before these writes may also corrupt another object, so privilege escalation cannot be excluded even though no arbitrary write primitive is proven. For the CVSS the PR:L value assumes a local user or process can generate traffic through an existing vulnerable TEQL and VLAN configuration. Creating the required qdisc topology normally requires CAP_NET_ADMIN. Direct remote reachability is not established and the specific network configuration raises attack complexity.
Mitigation
To mitigate this issue, prevent the sch_teql kernel module from loading by executing the following command as root:
# echo "install sch_teql /bin/true" >> /etc/modprobe.d/disable-sch_teql.conf
If the module is currently loaded and not in use, remove it:
# modprobe -r sch_teql
Warning: A system reboot may be required if the module is actively in use and cannot be unloaded. Disabling this module prevents the use of the True Equalizer (TEQL) queueing discipline, which may affect network setups that rely on this feature.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.5 | N/A | N/A |
| Attack Vector | Local | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | Low | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
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