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netfilter: conntrack: tcp: use UNACK timeout for non-closing RST packets

Assessment

Severity
Low
CVSS base score
3.7
Impact
Not stated
Exploitation detected
Unknown: not stated by MSRC
Exploitability
Not assessed
Publicly disclosed
Unknown: not stated by MSRC
EPSS · 30-day forecast
No EPSS score collected
Customer action
Required: follow the MSRC remediation guidance
More details
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Public detection template
No Nuclei template is listed in the current collected catalog
Component
Mariner
Weakness
—
Issued by
Linux
Published
9 Nov 2026 · November 2026
Last revised
9 Nov 2026
CVSS 3.1 base metricsRed raises the risk · green lowers it
Attack vector
NetworkAV:N
Attack complexity
HighAC:H
Privileges required
NonePR:N
User interaction
NoneUI:N
Scope
UnchangedS:U
Confidentiality
NoneC:N
Integrity
NoneI:N
Availability
LowA:L

Updates that fix it

0 KBs

No KB listed

No KB update is listed in the collected MSRC record. Check the MSRC advisory for product releases and other remedies.

Affected products

Open Source Software
1 affected product
  • azl3 kernel 6.6.161.1-1 on Azure Linux 3.0
Page history

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Cite this version
Field-level log (0)

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No retained field changes for this selection.

Explore global source statements, affected packages and advisory history for CVE-2026-99283. The catalog has a separate collection scope from Microsoft release records.

Collected exploitation and prediction evidence

Risk source coverage

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

cve-program · CVE-2026-99283

Published

netfilter: conntrack: tcp: use UNACK timeout for non-closing RST packets

In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: tcp: use UNACK timeout for non-closing RST packets Commit be0502a3f2e9 ("netfilter: conntrack: tcp: only close if RST matches exact sequence") keeps an established conntrack entry in ESTABLISHED when an in-window RST does not match the expected sequence number exactly, so the endpoint can validate the RST with a challenge ACK. The timeout selection nevertheless uses the CLOSE timeout for every RST packet. The bug is that timeout selection is based on the packet type, not on the state transition result: even when RST validation keeps new_state in ESTABLISHED, the timeout is still forced to TCP_CONNTRACK_CLOSE. Linux TCP independently rate limits challenge ACKs per socket. A second non-exact RST can therefore arrive after the first challenge ACK has restored the timeout but before the rate limit expires. The second RST lowers the timeout to 10 seconds again while the endpoint suppresses the second challenge ACK, allowing the conntrack entry to expire while both TCP endpoints remain established. Using the ESTABLISHED timeout for such RSTs would avoid this short expiration window, but it could also retain stale entries for the five-day default because conntrack cannot reliably match the endpoint's exact TCP state. Use the UNACK timeout for RST packets that leave the conntrack entry in TCP_CONNTRACK_ESTABLISHED. Exact-match RSTs and accepted RST packet trains still fall through to timeouts[new_state], which preserves the CLOSE timeout when conntrack accepts the RST as closing the flow. This avoids the aggressive 10-second expiration window for non-exact RSTs while preserving the short timeout for RSTs that conntrack accepts as closing the flow.

Source published
7 Nov 2026 20:14:11 UTC
Source modified
7 Nov 2026 20:14:11 UTC
Observed here
7 Nov 2026 21:52:05 UTC
Source terms
CVE Program Terms of Use

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ChangeIntel

An IT change radar: releases, security, known issues, retirements, documentation changes, and service status from public sources. Every item links to supporting evidence; dates and statuses can change after they are read.

Sources read 10 Nov 19:07 UTC · 261 of 275 readable · 260 fully read · documentation 469/469 current