LiveActive security incident?Get immediate response
CVE Record

CVE-2021-47590: mptcp: fix deadlock in __mptcp_push_pending()

In the Linux kernel, the following vulnerability has been resolved: mptcp: fix deadlock in __mptcp_push_pending() __mptcp_push_pending() may call mptcp_flush_join_list() with subflow socket lock held. If such call hits mptcp_sockopt_sync_all() then subsequently __mptcp_sockopt_sync() could try to lock the subflow socket for itself, causing a deadlock. sysrq: Show Blocked State task:ss-server state:D stack: 0 pid: 938 ppid: 1 flags:0x00000000 Call Trace: <TASK> __schedule+0x2d6/0x10c0 ? __mod_memcg_state+0x4d/0x70 ? csum_partial+0xd/0x20 ? _raw_spin_lock_irqsave+0x26/0x50 schedule+0x4e/0xc0 __lock_sock+0x69/0x90 ? do_wait_intr_irq+0xa0/0xa0 __lock_sock_fast+0x35/0x50 mptcp_sockopt_sync_all+0x38/0xc0 __mptcp_push_pending+0x105/0x200 mptcp_sendmsg+0x466/0x490 sock_sendmsg+0x57/0x60 __sys_sendto+0xf0/0x160 ? do_wait_intr_irq+0xa0/0xa0 ? fpregs_restore_userregs+0x12/0xd0 __x64_sys_sendto+0x20/0x30 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f9ba546c2d0 RSP: 002b:00007ffdc3b762d8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c RAX: ffffffffffffffda RBX: 00007f9ba56c8060 RCX: 00007f9ba546c2d0 RDX: 000000000000077a RSI: 0000000000e5e180 RDI: 0000000000000234 RBP: 0000000000cc57f0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f9ba56c8060 R13: 0000000000b6ba60 R14: 0000000000cc7840 R15: 41d8685b1d7901b8 </TASK> Fix the issue by using __mptcp_flush_join_list() instead of plain mptcp_flush_join_list() inside __mptcp_push_pending(), as suggested by Florian. The sockopt sync will be deferred to the workqueue.

UnknownCVSS not scoredNot KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-47590 is a Linux kernel MPTCP deadlock bug. Under specific MPTCP send-path conditions, a task can block while trying to lock a subflow socket it already holds. The main business concern is availability for systems actively using Multipath TCP, not data theft or code execution based on the provided sources.

Executive priority

Treat as an availability maintenance item for Linux fleets using MPTCP. Prioritize patch verification on production systems that rely on MPTCP or expose services using it. Urgency is lower where MPTCP is disabled or unused, based on the provided evidence.

Technical view

The flaw is in __mptcp_push_pending(). It may call mptcp_flush_join_list() while holding a subflow socket lock; if sockopt synchronization follows, __mptcp_sockopt_sync() can attempt to reacquire that socket lock and deadlock. The upstream fix uses __mptcp_flush_join_list() so sockopt sync is deferred to a workqueue.

Likely exposure

Exposure appears limited to Linux systems running affected kernels where MPTCP is enabled and used. The source lists affected Linux kernel version entries including 5.13, 5.15.11, and 5.16, but organizations should validate exact vendor backports and distro advisories.

Exploitation context

The bundle does not cite active exploitation, and KEV is false. The available evidence shows a kernel deadlock and blocked task trace during MPTCP send processing. It does not support claims of remote code execution, privilege escalation, or weaponized exploitation.

Researcher notes

The evidence supports a lock-order deadlock in the MPTCP send path. The fix changes internal flushing behavior to defer sockopt sync. The bundle lacks CVSS, CWE, exploit prerequisites, and distro-specific affected ranges, so validation should focus on kernel lineage and vendor backports.

Mitigation direction

  • Check your Linux distribution advisory for CVE-2021-47590 status.
  • Update to a kernel containing the referenced MPTCP deadlock fix.
  • If MPTCP is unnecessary, consider disabling it per vendor guidance.
  • Prioritize systems that actively provide or consume MPTCP traffic.

Validation and detection

  • Inventory Linux kernel versions and distro patch levels.
  • Confirm whether MPTCP is enabled and used on exposed systems.
  • Review kernel changelogs for the referenced stable commits.
  • Look for blocked tasks involving MPTCP send paths during incident review.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2021-47590 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
2ADP providers
3Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux1b3e7ede1365a24db1b4fd837e58a595f52fa4ad, 1b3e7ede1365a24db1b4fd837e58a595f52fa4adunaffected
LinuxLinux5.13, 0, 5.15.11, 5.16affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.