CVE-2026-53014 in Linux
Summary
by MITRE • 06/24/2026
In the Linux kernel, the following vulnerability has been resolved:
net/sched: act_mirred: fix wrong device for mac_header_xmit check in tcf_blockcast_redir
In tcf_blockcast_redir(), when iterating block ports to redirect packets to multiple devices, the mac_header_xmit flag is queried from the wrong device. The loop sends to dev_prev but queries dev_is_mac_header_xmit(dev) — which is the NEXT device in the iteration, not the one being sent to.
This causes tcf_mirred_to_dev() to make incorrect decisions about whether to push or pull the MAC header. When the block contains mixed device types (e.g., an ethernet veth and a tunnel device), intermediate devices get the wrong mac_header_xmit flag, leading to skb header corruption. In the worst case, skb_push_rcsum with an incorrect mac_len can exhaust headroom and panic.
The last device in the loop is handled correctly (line 365-366 uses dev_is_mac_header_xmit(dev_prev)), confirming this is a copy-paste oversight for the intermediate devices.
Fix by using dev_prev instead of dev for the mac_header_xmit query, consistent with the device actually being sent to.
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Analysis
by VulDB Data Team • 06/24/2026
The vulnerability exists within the Linux kernel's packet filtering and traffic control subsystem, specifically in the net/sched directory where the act_mirred action handles packet redirection operations. This flaw manifests in the tcf_blockcast_redir function which manages the redirection of packets to multiple network devices within a block configuration. The issue stems from improper device reference handling during iteration through block ports, creating a critical inconsistency between the device being operated upon and the device from which header information is being queried.
The technical root cause involves a copy-paste error in the packet processing loop where the code correctly identifies the target device for sending packets but incorrectly queries the MAC header transmission flag from a different device. When iterating through network devices within a block, the function maintains a dev_prev variable to track the previous device and uses it properly for the final device handling at line 365-366. However, during intermediate iterations, the code erroneously calls dev_is_mac_header_xmit(dev) instead of dev_is_mac_header_xmit(dev_prev), causing the system to retrieve header information from the next device in sequence rather than the device actually receiving the packet.
This misconfiguration leads to fundamental packet header corruption issues when dealing with mixed device types within the same block configuration, particularly affecting scenarios involving ethernet veth interfaces alongside tunnel devices. The incorrect MAC header flag causes the tcf_mirred_to_dev() function to make erroneous decisions regarding whether to push or pull MAC headers during packet processing. When the system attempts to adjust packet headers based on faulty information, it can result in severe memory corruption conditions, specifically triggering skb_push_rcsum operations with incorrect mac_len values that systematically consume available headroom space until system panic occurs.
The vulnerability aligns with CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write categories from the Common Weakness Enumeration catalog, representing a classic case of improper input validation leading to memory corruption. From an operational perspective, this flaw falls under ATT&CK technique T1059 Command and Scripting Interpreter, as it affects system-level packet processing mechanisms that could be exploited through crafted network traffic to cause denial of service or potentially arbitrary code execution. The impact extends beyond simple packet misrouting to threaten system stability through memory corruption vulnerabilities that can escalate into complete system crashes. The fix implements a straightforward but critical correction by ensuring the mac_header_xmit flag is queried from dev_prev rather than dev, aligning the device reference with the actual device being processed in each iteration step.
This vulnerability demonstrates the complexity of kernel networking subsystems where seemingly minor reference errors can cascade into severe operational impacts. The issue specifically affects traffic control operations using the mirred action for packet redirection, making it particularly relevant for network administrators managing complex routing scenarios and network virtualization environments. The fix addresses a fundamental design inconsistency in device context management during multi-device packet processing operations, ensuring that header information is consistently retrieved from the appropriate device context rather than from a subsequent device in the processing sequence.