VulnerabilityPublished 18 Oct 2026Updated 24 Oct 2026

CVE-2026-98549: Linux kernel · tcp: prevent collapsing skbs across boundary in rtx queue

Affects Linux kernelSource CVE Database V5

Not known to be exploited · CVSS 9.1 Critical · fixed in fc6d80eb504458d6416b75a94188b268c95c6533 : patch Linux kernel as a priority.

Data as of 26 Oct 2026, 14:18 UTC

CVSS 3.1 base score

9.1Critical

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 32% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in fc6d80eb504458d6416b75a94188b268c95c6533, 9e2a2f98e8c0197108c6d97a1fa43bfd89071c30, 08e835f5ec6e261c79d8c39f8618b3af29e3b0da +2

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

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

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
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 18 Oct 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.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ e8f69799810c32dd40c6724d829eccc70baad07f, < fc6d80eb504458d6416b75a94188b268c95c6533	Fixed in fc6d80eb504458d6416b75a94188b268c95c6533
LinuxLinux	Affected ≥ e8f69799810c32dd40c6724d829eccc70baad07f, < 9e2a2f98e8c0197108c6d97a1fa43bfd89071c30	Fixed in 9e2a2f98e8c0197108c6d97a1fa43bfd89071c30
LinuxLinux	Affected ≥ e8f69799810c32dd40c6724d829eccc70baad07f, < 08e835f5ec6e261c79d8c39f8618b3af29e3b0da	Fixed in 08e835f5ec6e261c79d8c39f8618b3af29e3b0da
LinuxLinux	Affected ≥ e8f69799810c32dd40c6724d829eccc70baad07f, < 7ba87509c54cd519e7ed362e0c85e8431f066a18	Fixed in 7ba87509c54cd519e7ed362e0c85e8431f066a18
LinuxLinux	Affected ≥ e8f69799810c32dd40c6724d829eccc70baad07f, < 1ae7aee395245874d797890380d9192bd858fb7e	Fixed in 1ae7aee395245874d797890380d9192bd858fb7e
LinuxLinux	Affected =4.18	Fixed in–

AI-suggested

A fix is available and has been applied in multiple Linux kernel commits. Users should update to a fixed kernel version that includes these patches. Since this is not a cloud service, manual patching is required. There are no vendor advisories indicating no action is needed or that the issue is already mitigated without patching.

Description

CVE-2026-98549 is a critical vulnerability in the Linux kernel's TCP implementation affecting version 4.18. It involves improper handling of socket buffers (skbs) in the retransmission queue, allowing skbs to be collapsed across encryption boundaries. This can cause retransmitted data to be sent in cleartext or cause connection stalls due to dropped packets by certain drivers. The issue is fixed in several commits providing defense in depth by improving skb collapse checks and fallback behavior.

Impact

The vulnerability can lead to retransmission of TCP data in cleartext despite encryption being enabled, compromising confidentiality. Additionally, it can cause connection stalls due to packet drops in TLS device offload scenarios. The CVSS score of 9.1 reflects a critical severity with network attack vector, low attack complexity, no privileges required, no user interaction, high confidentiality impact, no integrity impact, and high availability impact.

Summary

The vulnerability in the Linux kernel TCP stack arises from tcp_write_collapse_fence() not properly preventing skbs queued after a switch to device encryption from being merged with earlier skbs in the retransmission queue. This leads to two main issues: (1) for PSP devices, merged skbs retain a decrypted flag from earlier skbs, causing retransmissions to be sent unencrypted, and (2) for TLS device offload, merged skbs straddle start markers causing software fallback failures and packet drops in certain drivers, resulting in stalled connections. The fix involves falling back to tcp_rtx_queue_tail() when tcp_write_queue_tail() is NULL and adding checks to prevent collapsing skbs with mismatched decrypted states.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 09:42 UTC

Technical details

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