CVE-2025-21710Network attack vector

TCP service denial via stale receive-window state

Published Feb 27, 2025 · Updated Aug 5, 2026

Denial of service in the Linux kernel TCP stack allows remote attackers to indefinitely stall established connections under memory pressure. tcp_select_window advertises zero without updating rcv_wnd and rcv_wup, so __tcp_cleanup_rbuf repeatedly rejects the recovered window and never sends a reopening ACK. A routable TCP peer can induce the squeeze before application authentication; each affected connection can remain deadlocked and pin server resources.

CVSS severity8.2
High
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the Linux kernel TCP stack allows remote attackers to indefinitely stall established connections under memory pressure. tcp_select_window advertises zero without updating rcv_wnd and rcv_wup, so __tcp_cleanup_rbuf repeatedly rejects the recovered window and never sends a reopening ACK. A routable TCP peer can induce the squeeze before application authentication; each affected connection can remain deadlocked and pin server resources.

The record

CVE
CVE-2025-21710
Published
Feb 27, 2025
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-667, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 27, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=6.6
  2. Affected versionversion=e2142825c120d4317abf7160a0fc34b3de532586 <1dd823a46e25ffde1492c391934f69a9e5eb574f
  3. Affected versionversion=e2142825c120d4317abf7160a0fc34b3de532586 <8c670bdfa58e48abad1d5b6ca1ee843ca91f7303
  4. Affected versionversion=e2142825c120d4317abf7160a0fc34b3de532586 <b01e7ceb35dcb7ffad413da657b78c3340a09039
  5. Affected versionversion=e2142825c120d4317abf7160a0fc34b3de532586 <b4055e2fe96f4ef101d8af0feb056d78d77514ff

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=6.6; version=e2142825c120d4317abf7160a0fc34b3de532586 <1dd823a46e25ffde1492c391934f69a9e5eb574f; version=e2142825c120d4317abf7160a0fc34b3de532586 <8c670bdfa58e48abad1d5b6ca1ee843ca91f7303; version=e2142825c120d4317abf7160a0fc34b3de532586 <b01e7ceb35dcb7ffad413da657b78c3340a09039; version=e2142825c120d4317abf7160a0fc34b3de532586 <b4055e2fe96f4ef101d8af0feb056d78d77514ff

Published CVSS scores

8.2Linux Kernel CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
5.5UbuntuCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5SUSECVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-667Improper Locking
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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