CVE-2025-38227 Overview
CVE-2025-38227 is a use-after-free vulnerability [CWE-416] in the Linux kernel's Virtual Digital TV (vidtv) test driver. The flaw resides in vidtv_mux_init within drivers/media/test-drivers/vidtv/vidtv_mux.c. When Program Specific Information (PSI) initialization fails, the code continues execution and accesses the freed si member, producing a slab-use-after-free condition reported by syzbot. A local authenticated user interacting with the DVB (Digital Video Broadcasting) demux device can trigger the condition. The issue affects multiple stable Linux kernel branches and Debian Linux 11.
Critical Impact
Local attackers with low privileges can trigger a kernel-mode use-after-free, potentially leading to memory corruption, information disclosure, or privilege escalation on affected Linux systems.
Affected Products
- Linux Kernel (multiple stable branches, including 5.10 baseline and derivatives)
- Debian Linux 11 (Bullseye)
- Distributions shipping the vidtv test driver module (CONFIG_DVB_VIDTV)
Discovery Timeline
- 2025-07-04 - CVE-2025-38227 published to the National Vulnerability Database
- 2026-07-30 - Last updated in NVD database
Technical Details for CVE-2025-38227
Vulnerability Analysis
The vulnerability is a slab-use-after-free [CWE-416] in the Linux media test driver vidtv. Execution flows through vidtv_start_streaming into vidtv_mux_init, which calls vidtv_channel_si_init and ultimately vidtv_psi_pat_table_init to allocate PSI structures. When PSI initialization fails partway through, the allocated memory backing the si member is released, but vidtv_mux_init continues its subsequent flow into vidtv_mux_pid_ctx_init at line 78 of vidtv_mux.c. That function dereferences the freed si pointer, producing an 8-byte read of freed slab memory that KASAN (Kernel Address Sanitizer) flags. Reachability is through the DVB demux ioctl chain (dvb_dmxdev_filter_stop, dvb_dmxdev_feed_restart, dmx_section_feed_start_filtering), which is exposed to local processes that can open /dev/dvb/adapterX/demuxN.
Root Cause
The root cause is missing error-path termination after PSI initialization failure. The initialization routine does not propagate the failure to abort vidtv_mux_init; instead, execution proceeds and re-references the already-freed si object. The upstream fix terminates the subsequent process after si initialization fails, preventing the stale-pointer dereference.
Attack Vector
Exploitation requires local access with permission to open the DVB demux character device. The attacker triggers stream feed operations that invoke vidtv_mux_init, forcing the failure path in PSI initialization. Because the freed slab object can be reallocated between the free and the re-read, an attacker with a controllable spray primitive may influence kernel memory contents and achieve escalation. There is no remote or unauthenticated path.
No verified proof-of-concept exploit is published. The vulnerability was discovered through syzbot fuzzing of the DVB subsystem, and reproduction details are described in the upstream kernel commit references.
Detection Methods for CVE-2025-38227
Indicators of Compromise
- KASAN reports in kernel logs referencing vidtv_mux_pid_ctx_init or vidtv_mux_init with slab-use-after-free Read messages.
- Unexpected kernel crashes, oops entries, or dmesg panic traces originating from drivers/media/test-drivers/vidtv/.
- Unprivileged processes opening /dev/dvb/adapter*/demux* on systems where DVB hardware is not present, indicating use of the vidtv test module.
Detection Strategies
- Inventory hosts where the vidtv module is loaded (lsmod | grep vidtv) and where CONFIG_DVB_VIDTV is enabled in the running kernel configuration.
- Enable KASAN on test and staging kernels to surface stale-pointer dereferences before production exposure.
- Correlate auditd records of DVB device opens with process lineage to identify anomalous local access to media test devices.
Monitoring Recommendations
- Forward kernel ring buffer messages (journalctl -k) to a central log platform and alert on KASAN, BUG:, or use-after-free strings.
- Monitor loaded kernel modules across the fleet and flag vidtv on production systems where it has no operational purpose.
- Track kernel version drift against fixed stable releases to confirm patch coverage on all Linux endpoints and servers.
How to Mitigate CVE-2025-38227
Immediate Actions Required
- Apply the upstream kernel patches referenced in the stable tree commits (for example 1d5f88f05348, 685c18bc5a36, 72541cae73d0, 7e62be1f3b24, 9824e1732a16, e1d72ff111ec, f8c2483be6e8).
- Update Debian 11 systems using the Debian LTS Security Announcement (msg00007) and Debian LTS Security Announcement (msg00008).
- Restrict access to /dev/dvb/* device nodes to trusted users and groups until patches are deployed.
Patch Information
The fix is committed to the mainline Linux kernel and backported across supported stable branches. Distribution package managers deliver the fix through standard kernel updates. Review the upstream kernel commit for the exact source change that terminates initialization when PSI setup fails.
Workarounds
- Blacklist the vidtv module on systems that do not need the DVB virtual test driver by adding blacklist vidtv to /etc/modprobe.d/.
- Remove or tighten permissions on /dev/dvb/adapter*/demux* so only privileged users can invoke DVB demux ioctls.
- Disable the CONFIG_DVB_VIDTV build option when compiling custom kernels for production workloads that do not require media test drivers.
# Prevent the vulnerable vidtv module from loading
echo 'blacklist vidtv' | sudo tee /etc/modprobe.d/disable-vidtv.conf
sudo rmmod vidtv 2>/dev/null || true
sudo update-initramfs -u
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
