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CVE-2023-52881— tcp: do not accept ACK of bytes we never sent

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于TCP协议栈在处理ACK时，内核可能接受对从未发送过的字节ACK确认。

CVSS 9.8 · Critical EPSS 0.62% · P47

Affected Version Matrix 24

VendorProduct Version RangeStatus
Linux Linux 354e4aa391ed50a4d827ff6fc11e0667d0859b25< 69eae75ca5255e876628ac5cee9eaab31f644b57 affected
354e4aa391ed50a4d827ff6fc11e0667d0859b25< 458f07ffeccd17f99942311e09ef574ddf4a414a affected
354e4aa391ed50a4d827ff6fc11e0667d0859b25< 7ffff0cc929fdfc62a74b384c4903d6496c910f0 affected
354e4aa391ed50a4d827ff6fc11e0667d0859b25< b17a886ed29f3b70b78ccf632dad03e0c69e3c1a affected
354e4aa391ed50a4d827ff6fc11e0667d0859b25< 0d4e0afdd6658cd21dd5be61880411a2553fd1fc affected
354e4aa391ed50a4d827ff6fc11e0667d0859b25< 008b807fe487e0b15a3a6c39add4eb477f73e440 affected
354e4aa391ed50a4d827ff6fc11e0667d0859b25< 2087d53a66e97a5eb5d1bf558d5bef9e5f891757 affected
354e4aa391ed50a4d827ff6fc11e0667d0859b25< 3d501dd326fb1c73f1b8206d4c6e1d7b15c07e27 affected
… +16 more rows
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I. Basic Information for CVE-2023-52881

Vulnerability Information
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Vulnerability Title
tcp: do not accept ACK of bytes we never sent
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: tcp: do not accept ACK of bytes we never sent This patch is based on a detailed report and ideas from Yepeng Pan and Christian Rossow. ACK seq validation is currently following RFC 5961 5.2 guidelines: The ACK value is considered acceptable only if it is in the range of ((SND.UNA - MAX.SND.WND) <= SEG.ACK <= SND.NXT). All incoming segments whose ACK value doesn't satisfy the above condition MUST be discarded and an ACK sent back. It needs to be noted that RFC 793 on page 72 (fifth check) says: "If the ACK is a duplicate (SEG.ACK < SND.UNA), it can be ignored. If the ACK acknowledges something not yet sent (SEG.ACK > SND.NXT) then send an ACK, drop the segment, and return". The "ignored" above implies that the processing of the incoming data segment continues, which means the ACK value is treated as acceptable. This mitigation makes the ACK check more stringent since any ACK < SND.UNA wouldn't be accepted, instead only ACKs that are in the range ((SND.UNA - MAX.SND.WND) <= SEG.ACK <= SND.NXT) get through. This can be refined for new (and possibly spoofed) flows, by not accepting ACK for bytes that were never sent. This greatly improves TCP security at a little cost. I added a Fixes: tag to make sure this patch will reach stable trees, even if the 'blamed' patch was adhering to the RFC. tp->bytes_acked was added in linux-4.2 Following packetdrill test (courtesy of Yepeng Pan) shows the issue at hand: 0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3 +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0 +0 bind(3, ..., ...) = 0 +0 listen(3, 1024) = 0 // ---------------- Handshake ------------------- // // when window scale is set to 14 the window size can be extended to // 65535 * (2^14) = 1073725440. Linux would accept an ACK packet // with ack number in (Server_ISN+1-1073725440. Server_ISN+1) // ,though this ack number acknowledges some data never // sent by the server. +0 < S 0:0(0) win 65535 <mss 1400,nop,wscale 14> +0 > S. 0:0(0) ack 1 <...> +0 < . 1:1(0) ack 1 win 65535 +0 accept(3, ..., ...) = 4 // For the established connection, we send an ACK packet, // the ack packet uses ack number 1 - 1073725300 + 2^32, // where 2^32 is used to wrap around. // Note: we used 1073725300 instead of 1073725440 to avoid possible // edge cases. // 1 - 1073725300 + 2^32 = 3221241997 // Oops, old kernels happily accept this packet. +0 < . 1:1001(1000) ack 3221241997 win 65535 // After the kernel fix the following will be replaced by a challenge ACK, // and prior malicious frame would be dropped. +0 > . 1:1(0) ack 1001
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于TCP协议栈在处理ACK时，内核可能接受对从未发送过的字节ACK确认。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 354e4aa391ed50a4d827ff6fc11e0667d0859b25 ~ 69eae75ca5255e876628ac5cee9eaab31f644b57 -
Linux Linux 3.8 -

II. Public POCs for CVE-2023-52881

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III. Intelligence Information for CVE-2023-52881

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Other References for CVE-2023-52881 (7)

Same Patch Batch · Linux · 2024-05-29 · 4 CVEs total

CVE-2024-36016 7.8 HIGH tty: n_gsm: fix possible out-of-bounds in gsm0_receive()
CVE-2024-36015 ppdev: Add an error check in register_device
CVE-2024-36014 drm/arm/malidp: fix a possible null pointer dereference

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2023-52881

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