# CVE-2021-47593: linux: In the Linux kernel, the following vulnerability has been resolved:  mptcp: clear 'kern' flag from fallback sockets...

CVE-2021-47593 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47593, released June 19, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47593
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0025
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 19, 2024

## Description

In the Linux kernel, the following vulnerability has been resolved:  mptcp: clear 'kern' flag from fallback sockets  The mptcp ULP extension relies on sk->sk_sock_kern being set correctly: It prevents setsockopt(fd, IPPROTO_TCP, TCP_ULP, "mptcp", 6); from working for plain tcp sockets (any userspace-exposed socket).  But in case of fallback, accept() can return a plain tcp sk. In such case, sk is still tagged as 'kernel' and setsockopt will work.  This will crash the kernel, The subflow extension has a NULL ctx->conn mptcp socket:  BUG: KASAN: null-ptr-deref in subflow_data_ready+0x181/0x2b0 Call Trace:  tcp_data_ready+0xf8/0x370  [..]

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.15.15-1 | [DEBIAN-CVE-2021-47593](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47593.md) | Jun 19, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.15.15-1 | [DEBIAN-CVE-2021-47593](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47593.md) | Jun 19, 2024 |
| Linux | linux Debian 14 | 5.15.15-1 | [DEBIAN-CVE-2021-47593](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47593.md) | Jun 19, 2024 |

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