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CVE Record

CVE-2024-26921: inet: inet_defrag: prevent sk release while still in use

In the Linux kernel, the following vulnerability has been resolved: inet: inet_defrag: prevent sk release while still in use ip_local_out() and other functions can pass skb->sk as function argument. If the skb is a fragment and reassembly happens before such function call returns, the sk must not be released. This affects skb fragments reassembled via netfilter or similar modules, e.g. openvswitch or ct_act.c, when run as part of tx pipeline. Eric Dumazet made an initial analysis of this bug. Quoting Eric: Calling ip_defrag() in output path is also implying skb_orphan(), which is buggy because output path relies on sk not disappearing. A relevant old patch about the issue was : 8282f27449bf ("inet: frag: Always orphan skbs inside ip_defrag()") [..] net/ipv4/ip_output.c depends on skb->sk being set, and probably to an inet socket, not an arbitrary one. If we orphan the packet in ipvlan, then downstream things like FQ packet scheduler will not work properly. We need to change ip_defrag() to only use skb_orphan() when really needed, ie whenever frag_list is going to be used. Eric suggested to stash sk in fragment queue and made an initial patch. However there is a problem with this: If skb is refragmented again right after, ip_do_fragment() will copy head->sk to the new fragments, and sets up destructor to sock_wfree. IOW, we have no choice but to fix up sk_wmem accouting to reflect the fully reassembled skb, else wmem will underflow. This change moves the orphan down into the core, to last possible moment. As ip_defrag_offset is aliased with sk_buff->sk member, we must move the offset into the FRAG_CB, else skb->sk gets clobbered. This allows to delay the orphaning long enough to learn if the skb has to be queued or if the skb is completing the reasm queue. In the former case, things work as before, skb is orphaned. This is safe because skb gets queued/stolen and won't continue past reasm engine. In the latter case, we will steal the skb->sk reference, reattach it to the head skb, and fix up wmem accouting when inet_frag inflates truesize.

HighCVSS 7.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux kernel networking flaw can release a socket while transmitted IPv4 fragments still depend on it. On affected systems, a local low-privileged user may be able to trigger serious confidentiality, integrity, or availability impact. Exposure depends on kernel version and transmit-path fragment reassembly.

Executive priority

Treat this as a high-priority kernel maintenance issue, especially on multi-user, container-hosting, virtual-switching, or network-processing systems. Accelerate version verification and vendor-supported updates, but do not characterize it as an active exploitation emergency based on the supplied evidence.

Technical view

IPv4 defragmentation could orphan a fragmented packet's socket reference before output-path processing finished. Reassembly through netfilter or similar transmit-pipeline modules, including Open vSwitch and ct_act, could therefore leave downstream code using an invalid socket reference. The fix delays orphaning, preserves the socket when reassembly completes, and corrects memory accounting.

Likely exposure

Potentially exposed assets are Linux systems running affected kernels where IPv4 fragments are reassembled within transmit processing through netfilter, Open vSwitch, ct_act, or similar modules. The supplied affected-version data is unusually formatted, so confirm exact exposure against distribution advisories and applicable stable commits.

Exploitation context

The CVSS vector describes local access, low complexity, low privileges, no user interaction, and potentially high confidentiality, integrity, and availability impact. The supplied record is not in KEV, and the sources provide no evidence of active exploitation or public weaponization.

Researcher notes

The defect concerns socket lifetime and write-memory accounting during output-path fragment reassembly. Relevant code paths include ip_defrag(), skb_orphan(), ip_local_out(), and refragmentation handling. The source bundle lists multiple stable-kernel commits, but its flattened version list does not reliably express branch-specific affected and fixed boundaries.

Mitigation direction

  • Install the distribution-supported kernel update containing the applicable upstream stable fix.
  • Prioritize systems using transmit-path IPv4 reassembly through netfilter, Open vSwitch, ct_act, or similar modules.
  • If immediate updating is impossible, consult vendor guidance; the supplied sources name no supported temporary mitigation.
  • Reboot into the updated kernel where required by the operating system or vendor.

Validation and detection

  • Inventory running kernel versions and distribution package revisions across hosts, appliances, and network nodes.
  • Identify transmit paths using netfilter, Open vSwitch, ct_act, or comparable IPv4 fragment reassembly.
  • Match installed packages against vendor advisories or confirm inclusion of the applicable upstream stable commit.
  • After updating, verify the running kernel changed following reboot and repeat exposure checks.
Prepared
Confidence
medium
Sources
10

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

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CVE-2024-26921 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.8 (3.1)
Known Exploited
No
Published

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

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.

1CVSS vectors
3Timeline events
2ADP providers
9Source links

SSVC decision data

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

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.8CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.8High
CVSS 3.1 vector shape for CVE-2024-26921Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

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

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux7026b1ddb6b8d4e6ee33dc2bd06c0ca8746fa7ab, 7026b1ddb6b8d4e6ee33dc2bd06c0ca8746fa7ab, 7026b1ddb6b8d4e6ee33dc2bd06c0ca8746fa7ab, 7026b1ddb6b8d4e6ee33dc2bd06c0ca8746fa7ab, 7026b1ddb6b8d4e6ee33dc2bd06c0ca8746fa7ab, 7026b1ddb6b8d4e6ee33dc2bd06c0ca8746fa7ab, 7026b1ddb6b8d4e6ee33dc2bd06c0ca8746fa7abunaffected
LinuxLinux4.1, 0, 5.4.285, 5.10.227, 5.15.168, 6.1.85, 6.6.26, 6.8.5, 6.9affected
Weakness

CWE details

No CWE listed

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