VulnerabilityPublished 28 Oct 2026

CVE-2026-99139: Linux kernel · TCP_CONGESTION

Source GCVE Database

Authoritative record:CVE-2026-99139

Not known to be exploited · fixed in c1804ef016392dd91267d2207ee43b1de34302ca : patch Linux kernel soon.

Data as of 28 Oct 2026, 14:02 UTC

Severity

High

Rated High by Threat Radar's AI analysis · CVSS not yet scored by NVD

Patch: Available – fixed in c1804ef016392dd91267d2207ee43b1de34302ca, a8e45471afa230c1431c26c8e99ec24377e3b514, 5271b79b7ad68dcb222e893773f92bdabf7750f3

Exploitation evidence

Disclosed: evidence found.
CVE published 28 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.

ghsa-48cq-p2fm-8444

What to do

Upgrade Linux kernel to c1804ef016392dd91267d2207ee43b1de34302ca, a8e45471afa230c1431c26c8e99ec24377e3b514 or 5271b79b7ad68dcb222e893773f92bdabf7750f3.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 0baf26b0fcd74bbfcef53c5d5e8bad2b99c8d0d2, < c1804ef016392dd91267d2207ee43b1de34302ca	Fixed in c1804ef016392dd91267d2207ee43b1de34302ca
LinuxLinux	Affected ≥ 0baf26b0fcd74bbfcef53c5d5e8bad2b99c8d0d2, < a8e45471afa230c1431c26c8e99ec24377e3b514	Fixed in a8e45471afa230c1431c26c8e99ec24377e3b514
LinuxLinux	Affected ≥ 0baf26b0fcd74bbfcef53c5d5e8bad2b99c8d0d2, < 5271b79b7ad68dcb222e893773f92bdabf7750f3	Fixed in 5271b79b7ad68dcb222e893773f92bdabf7750f3
LinuxLinux	Affected =5.6	Fixed in–

AI-suggested

A fix is available that properly synchronizes access to the congestion control operations pointer using rcu_read_lock() and memory access annotations. Users should apply the official Linux kernel patches that address this issue. Since this is a kernel vulnerability, updating to a fixed kernel version is the recommended remediation.

Description

A use-after-free vulnerability in the Linux kernel's TCP implementation was fixed in the do_tcp_getsockopt function when handling TCP_CONGESTION. The flaw involved reading a pointer to congestion control operations without proper synchronization, which could lead to accessing freed memory. The issue was addressed by adding appropriate locking and memory access annotations to prevent concurrent use-after-free and data races.

Impact

The vulnerability could cause kernel memory corruption due to use-after-free, potentially leading to system instability or crashes. There is no indication of known exploitation in the wild. The flaw affects the Linux kernel's TCP congestion control option handling, which could be triggered by local or privileged users manipulating socket options.

Summary

CVE-2026-99139 describes a use-after-free vulnerability in the Linux kernel's TCP stack, specifically in the do_tcp_getsockopt function handling TCP_CONGESTION. The function read icsk->icsk_ca_ops->name without holding the required rcu_read_lock(), introduced after a commit that allowed icsk_ca_ops to point to dynamically allocated BPF struct_ops memory. This memory could be freed concurrently via setsockopt(TCP_CONGESTION), leading to a use-after-free condition and potential kernel memory corruption. The fix involved holding rcu_read_lock() during access, using READ_ONCE() to safely load the pointer, copying the name to a stack buffer before releasing the lock, and annotating stores with WRITE_ONCE() to address related data races.

References

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