Critical

Linux kernel TLS use-after-free race in tls_sw_cancel_work_tx()

IdentifiersCVE-2026-23240CWE-416

CVE-2026-23240 is a Linux kernel TLS subsystem vulnerability caused by a race condition in tls_sw_cancel_work_tx(). During socket teardown, tls_sk_proto_close() calls tls_sw_cancel_work_tx() and uses cancel_delayed_work_sync() to stop pending TX work. However, tx_work_handler() can still be rescheduled concurrently from other execution paths, including tls_write_space()/tls_sw_write_space(), such as via the Delayed ACK handler or ksoftirqd. In the documented race, one CPU is closing the TLS socket and cancelling delayed work while another CPU sets BIT_TX_SCHEDULED and schedules tx_work.work again. This can result in tx_work_handler() running after the associated TLS object has been freed, leading to a use-after-free/dangling-pointer dereference. The upstream fix replaces cancel_delayed_work_sync() with disable_delayed_work_sync() to prevent the delayed work from being rescheduled during teardown.

For your environment

Are you exposed to this one?

Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.

Start free trial

ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful triggering of the race can cause the kernel worker tx_work_handler() to dereference a freed TLS object, resulting in kernel memory corruption and likely system instability or crash. Because this is a kernel use-after-free in a network-facing subsystem and the provided context lists a CVSS v3.1 vector of AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, the potential impact includes denial of service and, depending on exploitability in a given environment, possible arbitrary code execution in kernel context with consequent compromise of confidentiality, integrity, and availability.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, reduce exposure by limiting use of the kernel TLS subsystem on affected systems, especially for untrusted or externally reachable network workloads that can exercise TLS socket teardown and TX scheduling paths. Minimize network exposure to affected services, restrict access to trusted peers where feasible, and prefer configurations that do not rely on kernel TLS offload/software TLS paths until patched. These are temporary risk-reduction measures only; no complete mitigation is provided in the context aside from updating to a fixed kernel.

Remediation

Patch, then assume compromise.

Apply a kernel update that includes the upstream fix for CVE-2026-23240. The fix changes the TLS TX work cancellation logic by replacing cancel_delayed_work_sync() with disable_delayed_work_sync() in the affected teardown path. Vendor advisories indicate fixed packages are available in multiple SUSE kernel branches, including for example kernel-default >= 6.12.0-160000.28.1 on SLES 16.0, kernel-default >= 6.4.0-150600.23.112.1 on SLES 15 SP6, kernel-default >= 5.14.21-150500.55.166.1 on SLES 15 SP5, kernel-default >= 5.14.21-150400.24.219.1 on SLES 15 SP4, and kernel-default >= 6.4.0-46.1 on SLE Micro 6.0. Reboot after installing the updated kernel.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

LinuxLinux Kerneloperating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

8 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

8 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

Start free trial

Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-23240

NVD

nvd.nist.gov/vuln/detail/CVE-2026-23240

MITRE CWE · CWE-416

cwe.mitre.org

Patch

git.kernel.org/stable/c/17153f154f80be2b47ebf52840f2d8f724eb2f3b

Patch

git.kernel.org/stable/c/7bb09315f93dce6acc54bf59e5a95ba7365c2be4

Patch

git.kernel.org/stable/c/854cd32bc74fe573353095e90958490e4e4d641b

Patch

git.kernel.org/stable/c/a5de36d6cee74a92c1a21b260bc507e64bc451de