5.5

CVE-2021-4442: tcp: add sanity tests to TCP_QUEUE_SEQ

Analyzed
AliasesUBUNTU-CVE-2021-4442DEBIAN-CVE-2021-4442
Published 29-08-2024Last modified 11-05-2026

Vulnerability summary

CVE-2021-4442 is a medium (CVSS 5.5) vulnerability in linux. EPSS estimates a 0.39% chance of exploitation in the next 30 days, higher than 33.5% of scored vulnerabilities. 5 public exploits are recorded.

Priority
Routine

Not severe (CVSS 5.5, local access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
5.5/10
010
Medium · v3.1 (NVD)
EPSS score
0.39%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits5reference

Advisory lineage

Upstream 0 · Downstream 2 · Related 1
RHSA-2021:4356SUSE-SU-2024:3566-1

Timeline

  1. 29-08-2024
    PublishedVulnerability first disclosed.
  2. 11-05-2026
    Last modifiedVulnerability information updated.

Description

In the Linux kernel, the following vulnerability has been resolved: tcp: add sanity tests to TCP_QUEUE_SEQ Qingyu Li reported a syzkaller bug where the repro changes RCV SEQ _after_ restoring data in the receive queue. mprotect(0x4aa000, 12288, PROT_READ) = 0 mmap(0x1ffff000, 4096, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x1ffff000 mmap(0x20000000, 16777216, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x20000000 mmap(0x21000000, 4096, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x21000000 socket(AF_INET6, SOCK_STREAM, IPPROTO_IP) = 3 setsockopt(3, SOL_TCP, TCP_REPAIR, [1], 4) = 0 connect(3, {sa_family=AF_INET6, sin6_port=htons(0), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_scope_id=0}, 28) = 0 setsockopt(3, SOL_TCP, TCP_REPAIR_QUEUE, [1], 4) = 0 sendmsg(3, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="0x0000000000000003\0\0", iov_len=20}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 20 setsockopt(3, SOL_TCP, TCP_REPAIR, [0], 4) = 0 setsockopt(3, SOL_TCP, TCP_QUEUE_SEQ, [128], 4) = 0 recvfrom(3, NULL, 20, 0, NULL, NULL) = -1 ECONNRESET (Connection reset by peer) syslog shows: [ 111.205099] TCP recvmsg seq # bug 2: copied 80, seq 0, rcvnxt 80, fl 0 [ 111.207894] WARNING: CPU: 1 PID: 356 at net/ipv4/tcp.c:2343 tcp_recvmsg_locked+0x90e/0x29a0 This should not be allowed. TCP_QUEUE_SEQ should only be used when queues are empty. This patch fixes this case, and the tx path as well.

CVSS metrics

4 scores · 3 sources · 2 versions

EPSS trend

Probability

0.39%

Chance of exploitation in the next 30 days

Percentile

34%

Versus all other CVEs

30-day change

No change 0.00 pp

From 0.39% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

5 found
  • referenceUnverified

    Exploit Reference (git.kernel.org)

    Maturity: unknown

  • referenceUnverified

    Exploit Reference (git.kernel.org)

    Maturity: unknown

  • referenceUnverified

    Exploit Reference (git.kernel.org)

    Maturity: unknown

Show all 5 exploits
  • referenceUnverified

    Exploit Reference (git.kernel.org)

    Maturity: unknown

  • referenceUnverified

    Exploit Reference (git.kernel.org)

    Maturity: unknown

Weaknesses

CWE · root cause

No weakness data has been published for this record.

Affected systems

Version check

Known conditions: local access, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.

Ubuntu94 products
  • linuxAll versions (No fix recorded) | < 4.15.0-144.148 | < 5.4.0-73.82
  • linux-allwinner-5.19All versions (No fix recorded)
  • linux-awsAll versions (No fix recorded) | < 4.15.0-1103.110 | < 5.4.0-1048.50
  • linux-aws-5.0All versions (No fix recorded)
  • linux-aws-5.11All versions (No fix recorded)
Linux2 products
  • linux≥ ee9952831cfd0bbe834f4a26489d7dce74582e37, < 319f460237fc2965a80aa9a055044e1da7b3692a | ≥ ee9952831cfd0bbe834f4a26489d7dce74582e37, < 3bf899438c123c444f6b644a57784dfbb6b15ad6 | ≥ ee9952831cfd0bbe834f4a26489d7dce74582e37, < 046f3c1c2ff450fb7ae53650e9a95e0074a61f3e | ≥ ee9952831cfd0bbe834f4a26489d7dce74582e37, < 3b72d5a703842f582502d97906f17d6ee122dac2 | ≥ ee9952831cfd0bbe834f4a26489d7dce74582e37, < 8811f4a9836e31c14ecdf79d9f3cb7c5d463265d | 3.5
  • linux_kernel≥ 3.5, < 4.19.181 | ≥ 4.20, < 5.4.106 | ≥ 5.5, < 5.10.24 | ≥ 5.11, < 5.11.7 | 5.12:rc1 | 5.12:rc2
Debian1 product
  • linux< 5.10.24-1

3 vendors · 97 products

References

9 links