CVE-2021-47591: mptcp: remove tcp ulp setsockopt support

Recommended actionScheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available

What, why and how

In the Linux kernel, the following vulnerability has been resolved: mptcp: remove tcp ulp setsockopt support TCP_ULP setsockopt cannot be used for mptcp because its already used internally to plumb subflow (tcp) sockets to the mptcp layer. syzbot managed to trigger a crash for mptcp connections that are in fallback mode: KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027] CPU: 1 PID: 1083 Comm: syz-executor.3 Not tainted 5.16.0-rc2-syzkaller #0 RIP: 0010:tls_build_proto net/tls/tls_main.c:776 [inline] [..] __tcp_set_ulp net/ipv4/tcp_ulp.c:139 [inline] tcp_set_ulp+0x428/0x4c0 net/ipv4/tcp_ulp.c:160 do_tcp_setsockopt+0x455/0x37c0 net/ipv4/tcp.c:3391 mptcp_setsockopt+0x1b47/0x2400 net/mptcp/sockopt.c:638 Remove support for TCP_ULP setsockopt.

What

Why

The product dereferences a pointer that it expects to be valid but is NULL.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

What

Why

The product dereferences a pointer that it expects to be valid but is NULL.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation

Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.

No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material

Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.

None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path: local access → NULL Pointer Dereference → disrupt the affected service
Attack surface: Local
Privileges required: Low: a basic authenticated account is required
User interaction: None
Attack complexity: Low: no specialised conditions are recorded
Security boundary: Unchanged: impact remains within the vulnerable component's security authority
Weakness ? CWE means Common Weakness Enumeration: a standard category for the underlying weakness.: CWE-476 ↗
CWE-476: NULL Pointer Dereference. The product dereferences a pointer that it expects to be valid but is NULL.
CVSS vector ? CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land: The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.

Denial of serviceCWE-476

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2021-34593Official EUVD mapping

0 linked advisory records.

Official EUVD record ↗

BSI · German · WID-SEC-2024-1418Linux Kernel: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff

Ein lokaler Angreifer kann mehrere Schwachstellen im Linux Kernel ausnutzen, um einen nicht näher spezifizierten Angriff durchzuführen.

Official advisory ↗

CERT-FR · French · CERTFR-2024-AVI-0717Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47520 Référence CVE CVE-2021-47542 https://www.cve.org/CVERecord?id=CVE-2021-47542 Référence CVE CVE-2021-47546 https://www.cve.org/CVERecord?id=CVE-2021-47546 Référence CVE CVE-2021-47547 https://www.cve.org/CVERecord?id=CVE-2021-47547 Référence CVE CVE-2021-47559 https://www.cve.org/CVERecord?id=CVE-2021-47559 Référence CVE CVE-2021-47580 https://www.cve.org/CVERecord?id=CVE-2021-47580 Référence CVE CVE-2021-47582 https://www.cve.org/CVERecord?id=CVE-2021-47582 Référence CVE CVE-2021-47588 https://www.cve.org/CVERecord?id=CVE-2021-47588 Référence CVE CVE-2021-47590 https://www.cve.org/CVERecord?id=CVE-2021-47590 Référence CVE CVE-2021-47591 https://www.cve.org/CVERecord?id=CVE-2021-47591 Référence CVE CVE-2021-47593 https://www.cve.org/CVERecord?id=CVE-2021-47593 Référence CVE CVE-2021-47597 https://www.cve.org/CVERecord?id=CVE-2021-47597 Référence CVE CVE-2021-47598 https://www.cve.org/CVERecord?id=CVE-2021-47598 Référence CVE CVE-2021-47599 https://www.cve.org/CVERecord?id=CVE-2021-47599 Référence CVE CVE-2021-47600 https://www.cve.org/CVERecord?id=CVE-2021-47600 Référence CVE CVE-2021-47606 https://www.cve.org/CVERecord?id=CVE-2021-47606 Référence CVE CVE-2021-47619 https://www.cve.org/CVERecord?id=CVE-2021-47619 Référence CVE CVE-2021-47622 https://www.cve.org/CVERecord?id=

Official advisory ↗

CERT-FR · French · CERTFR-2024-AVI-0693Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47582 Référence CVE CVE-2021-47583 https://www.cve.org/CVERecord?id=CVE-2021-47583 Référence CVE CVE-2021-47584 https://www.cve.org/CVERecord?id=CVE-2021-47584 Référence CVE CVE-2021-47585 https://www.cve.org/CVERecord?id=CVE-2021-47585 Référence CVE CVE-2021-47586 https://www.cve.org/CVERecord?id=CVE-2021-47586 Référence CVE CVE-2021-47587 https://www.cve.org/CVERecord?id=CVE-2021-47587 Référence CVE CVE-2021-47588 https://www.cve.org/CVERecord?id=CVE-2021-47588 Référence CVE CVE-2021-47589 https://www.cve.org/CVERecord?id=CVE-2021-47589 Référence CVE CVE-2021-47590 https://www.cve.org/CVERecord?id=CVE-2021-47590 Référence CVE CVE-2021-47591 https://www.cve.org/CVERecord?id=CVE-2021-47591 Référence CVE CVE-2021-47592 https://www.cve.org/CVERecord?id=CVE-2021-47592 Référence CVE CVE-2021-47593 https://www.cve.org/CVERecord?id=CVE-2021-47593 Référence CVE CVE-2021-47595 https://www.cve.org/CVERecord?id=CVE-2021-47595 Référence CVE CVE-2021-47596 https://www.cve.org/CVERecord?id=CVE-2021-47596 Référence CVE CVE-2021-47597 https://www.cve.org/CVERecord?id=CVE-2021-47597 Référence CVE CVE-2021-47598 https://www.cve.org/CVERecord?id=CVE-2021-47598 Référence CVE CVE-2021-47599 https://www.cve.org/CVERecord?id=CVE-2021-47599 Référence CVE CVE-2021-47600 https://www.cve.org/CVERecord?id=

Official advisory ↗

Patch and workaround

Operational remediation based on structured source evidence.

Status ? Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.: Patch available
Affected: Linux: d9e4c129181004ec94b315b0c9db5eeb09da75e6 < 3de0c86d42f841d1d64f316cd949e65c566f0734, d9e4c129181004ec94b315b0c9db5eeb09da75e6 < 404cd9a22150f24acf23a8df2ad0c094ba379f57, 5.13
Fixed: Linux: < 5.13, 5.15.11 ≤ 5.15.*, 5.16 ≤ *
Action: Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround: No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.

Evidence and provenance

Published 19 Jun 2024 · Last source change 11 May 2026, 13:57 UTC · CWE-476 · NULL Pointer Dereference

CVE recordCVE.org · 5.2

CVSS sourceNIST NVD

EPSS source

The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.

FIRST · tracked since 2026-08-14

European sourceENISA EUVD · EUVD-2021-34593

Product sourceCNA

Remediation sourceCVE/CNA references

CWE sourceNIST NVD

NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

2024-06-19CVE published

2026-05-11Fixed release or patch reference recorded

ENISA EUVD · EUVD-2021-34593↗CVE authority or vendor reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗

Technical terms and abbreviations used in this report

CVE: Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS: Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS: Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE: Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA: CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP: Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD: National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT: A computer security incident response team that publishes warnings or coordinates incident response.
PoC: Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF: Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL: Living off the land: abuse of legitimate tools or system functions during an attack.

mptcp: remove tcp ulp setsockopt support

National CERT insights
?
CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

ENISA European Vulnerability Database

EUVD-2021-34593

What, why and how

Exploit reality and attack path

Official authority intelligence

Patch and workaround

Evidence and provenance

What changed after publication

mptcp: remove tcp ulp setsockopt support

National CERT insights ?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

EUVD-2021-34593

What, why and how

Exploit reality and attack path

Official authority intelligence

Patch and workaround

Evidence and provenance

National CERT insights
?
CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.