VulnerabilityPublished 1 Jul 2026Updated 22 Jul 2026

CVE-2026-53349: Linux kernel · netfilter: nf_conntrack: destroy stale expectfn expectations on unregister

Source GCVE Database

Not known to be exploited · CVSS 5.5 Medium.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

5.5Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 1% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Local
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 1 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 Oct 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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.

ghsa-qf7g-7vpq-493r

What to do

AI-suggested

A fix has been implemented in the Linux kernel to properly destroy stale expectations during NAT helper module unregistering, preventing use-after-free crashes. Users should update to a Linux kernel version that includes this fix. Since this requires kernel module unloading privileges, limiting CAP_SYS_MODULE access reduces risk. Patch status is not explicitly stated here; check the vendor or Linux kernel advisories for the fixed kernel versions and apply updates accordingly.

Description

A vulnerability in the Linux kernel's netfilter nf_conntrack subsystem could cause a use-after-free condition when NAT helpers unregister while expectations still exist. This occurs because stale pointers to module code remain in the expectation table after module removal, leading to kernel crashes when those pointers are dereferenced. The issue requires CAP_SYS_MODULE privileges to exploit and is considered a robustness flaw rather than a direct attack vector.

Impact

The vulnerability can cause a kernel crash (denial of service) due to use-after-free when a NAT helper module is removed while expectations still exist. Exploitation requires CAP_SYS_MODULE privileges to unload the module, so it is primarily a robustness issue rather than a remote code execution or privilege escalation risk. No confidentiality or integrity impacts are reported.

Summary

The Linux kernel netfilter nf_conntrack subsystem had a flaw where NAT helpers like nf_nat_h323 stored raw pointers to module text in expectation callbacks (exp->expectfn). When a NAT helper module is unregistered, the callback descriptor is unlinked but the expectation table is not walked to remove stale expectations. This leaves dangling pointers to freed module code. When an expected connection arrives, the kernel calls the stale exp->expectfn pointer, causing a kernel crash (use-after-free). The fix introduces nf_ct_helper_expectfn_destroy(), which walks the expectation table and removes any expectations referencing the torn-down module after the RCU grace period, preventing use-after-free crashes.

References

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