CVE-2025-39766VulnerabilityPublished 21 Apr 2026Updated 9 Nov 2026

Red Hat Security Advisory: kernel security update

Affects Linux kernelSource GCVE Database

Compare

Mentioned vulnerabilities

Not known to be exploited · patch available : patch Linux kernel soon.

Data as of 10 Nov 2026, 00:33 UTC

Severity

High

Rated by Threat Radar · No CVSS score from NVD or the CNA

EPSS: 0.1% chance of exploitation in 30 days – higher than 8% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Red Hat Product Security Red Hat	Affected Red Hat Red Hat Enterprise Linux Red Hat Enterprise Linux AppStream E4S (v.9.2) Red Hat Enterprise Linux BaseOS E4S (v.9.2) aarch64 Red Hat Enterprise Linux Real Time E4S (v.9.2) Red Hat Enterprise Linux Real Time for NFV E4S (v.9.2) src SUSE noarch kernel-abi-stablelists-6.12.0-124.52.1.el10_1.noarch kernel-doc-6.12.0-124.52.1.el10_1.noarch x86_64 Red Hat Enterprise Linux AppStream (v. 10) Red Hat Enterprise Linux BaseOS (v. 10) Red Hat Enterprise Linux CodeReady Linux Builder (v. 10)	Fixed in–

AI-suggested

A security update is available from Red Hat and should be applied promptly. The update requires a system reboot to take effect. Users should upgrade to the fixed kernel versions as specified in the Red Hat advisory RHSA-2026:9264. No additional mitigation steps are indicated beyond applying the official patch and rebooting.

Description

The kernel-rt packages provide the Real Time Linux Kernel, which enables fine-tuning for systems with extremely high determinism requirements. Security Fix(es): * kernel: net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit (CVE-2025-39766) * kernel: Linux kernel: Use-after-free in traffic control (act_ct) may lead to denial of service or privilege escalation (CVE-2026-23270) * kernel: Linux kernel: Use-after-free in bonding driver leads to denial of service (CVE-2026-31419) * kernel: ip6_tunnel: clear skb2->cb[] in ip4ip6_err() (CVE-2026-43037) * kernel: ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach() (CVE-2026-43038) * kernel: smb: client: validate the whole DACL before rewriting it in cifsacl (CVE-2026-31709) * kernel: md/bitmap: fix GPF in write_page caused by resize race (CVE-2026-43163) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Impact

The vulnerabilities could allow an attacker to cause denial of service or escalate privileges on affected systems by exploiting use-after-free conditions and improper buffer handling in kernel networking and driver components. The issues affect core kernel functionality, potentially impacting system stability and security.

Summary

This advisory covers several security fixes in the Linux kernel packages provided by Red Hat, including CVE-2025-39766 where the net/sched subsystem's cake_enqueue function is modified to return NET_XMIT_CN when past buffer_limit, and other use-after-free vulnerabilities in traffic control and bonding drivers (CVE-2026-23270, CVE-2026-31419). Additional fixes address issues in IPv6 tunneling, SMB client DACL validation, and md/bitmap race conditions. These vulnerabilities impact multiple kernel subsystems and architectures across Red Hat Enterprise Linux 10 and related products. The advisory confirms patch availability and recommends updating to fixed kernel versions.

CWE-390Detection of Error Condition Without Action (opens in a new tab)
Base weaknessLikelihood of exploit: MediumOWASP Top 10 A10:2025: Mishandling of Exceptional Conditions (opens in a new tab)
The product detects a specific error, but takes no actions to handle the error.
Implementation
Properly handle each exception. This is the recommended solution. Ensure that all exceptions are handled in such a way that you can be sure of the state of your system at any given moment.
Implementation
If a function returns an error, it is important to either fix the problem and try again, alert the user that an error has happened and let the program continue, or alert the user and close and cleanup the program.
Testing
Subject the product to extensive testing to discover some of the possible instances of where/how errors or return values are not handled. Consider testing techniques such as ad hoc, equivalence partitioning, robustness and fault tolerance, mutation, and fuzzing.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Logging (opens in a new tab)
Error Handling (opens in a new tab)
OWASP ASVS 4.0.3
V11.1.8 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-763Release of Invalid Pointer or Reference (opens in a new tab)
Base weakness
The product attempts to return a memory resource to the system, but it calls the wrong release function or calls the appropriate release function incorrectly.
Implementation
Only call matching memory management functions. Do not mix and match routines. For example, when you allocate a buffer with malloc(), dispose of the original pointer with free().
Implementation
When programming in C++, consider using smart pointers provided by the boost library to help correctly and consistently manage memory.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-416Use After Free (opens in a new tab)
Variant weaknessLikelihood of exploit: HighCWE Top 25 (2025): #7
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
Architecture and Design · Language Selection
Choose a language that provides automatic memory management.
Implementation · Attack Surface Reduction
When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-1288Improper Validation of Consistency within Input (opens in a new tab)
Base weakness
The product receives a complex input with multiple elements or fields that must be consistent with each other, but it does not validate or incorrectly validates that the input is actually consistent.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-843Access of Resource Using Incompatible Type (Type Confusion) (opens in a new tab)
Base weakness
The product allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.
CWE-825Expired Pointer Dereference (opens in a new tab)
Base weakness
The product dereferences a pointer that contains a location for memory that was previously valid, but is no longer valid.
Architecture and Design
Choose a language that provides automatic memory management.
Implementation
When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 11 Aug 2026, 20:36 UTC

WeaknessesCWE-390, CWE-763, CWE-416 +3

Technical details

References

Community reviews

Related threats