CVE-20XX-?
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CVE-2023-52881

9.8 CRITICAL 0.6% exploit odds Fix listed Other OS & kernel

What it is

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

At a glance

Exploitability
Can be exploited over the network without logging in. High risk of data exposure, data tampering, service disruption.
Exploit odds
0.6% chance of exploitation in the next 30 days (EPSS).
Fix
A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

  1. PublishedDisclosed publicly on CVE.org and NVD
  2. Last updatedMost recent change to the record

Why it ranks here

Details

Published
Last modified
Exploit probability
0.6% · EPSS, next 30 days
Record status
Modified

Affected

Attack profile CVSS 3.1 · 9.8

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Raw vector

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

Is it in your code?

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Read https://cve-list.com/agent/cve/CVE-2023-52881.md and follow it. Check whether this project is affected by CVE-2023-52881. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record