CVE-2024-26921

Published Apr 18, 2024

Last updated 6 months ago

CVSS medium 5.5
Ubuntu

Overview

Description
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.
Source
416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD status
Modified
Products
linux_kernel

Risk scores

CVSS 3.1

Type
Primary
Base score
5.5
Impact score
3.6
Exploitability score
1.8
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Severity
MEDIUM

Weaknesses

nvd@nist.gov
NVD-CWE-noinfo

Social media

Hype score
Not currently trending

  1. URGENT: Critical kernel vulnerability (CVE-2024-26921) patched in #SUSE Linux Enterprise Server. This high-severity flaw allows local privilege escalation. Read more: 👉 https://t.co/8HP77JLKln #Security https://t.co/GwrHrmtACf

    @Cezar_H_Linux

    2 Nov 2025

    62 Impressions

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  2. 🔐 Critical #Ubuntu kernel patch released: USN-7820-1. Patches CVE-2024-26921 (Netfilter priv esc) & CVE-2024-26922 (ACPI info leak). Affects 22.04 LTS / 23.10. Read more: 👉 https://t.co/HCr3STWxLS #Security https://t.co/bhTXEtoYXF

    @Cezar_H_Linux

    13 Oct 2025

    8 Impressions

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  3. 🚨 Critical kernel update for #Ubuntu 22.04 LTS! CVE-2024-26921 (Local Privilege Escalation) & CVE-2024-26922 (Remote DoS) patched. Affects Intel i915 driver & network scheduler. Read more: 👉 https://t.co/2rrSF6H5D4 #Security https://t.co/E1UwiwAwHK

    @Cezar_H_Linux

    7 Oct 2025

    47 Impressions

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  4. 🚨 Urgent for #Azure users: Critical Linux kernel vuln patched in Ubuntu (CVE-2024-26921). Allows local privilege escalation to root. Read more: 👉 https://t.co/zLo6zE9JVj #Security https://t.co/hqR5Bdguip

    @Cezar_H_Linux

    3 Oct 2025

    69 Impressions

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  5. 🚨 Critical Linux kernel vulnerabilities patched in #Ubuntu (USN-7715-1). Affects CVE-2024-26921, CVE-2024-26878, and others. Read more: 👉 https://t.co/6JD2s8sTZN #Security https://t.co/ltOmO2CWXJ

    @Cezar_H_Linux

    27 Aug 2025

    102 Impressions

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  6. #Kernel_Security 1. Cross Cache Attack CheetSheet - https://t.co/XvNeAADKRX 2. Linux KASLR Entropy - https://t.co/wcMRVVvRio 3. Some Casual Notes for CVE-2024-26921 - https://t.co/45fhKGk9ky 4. The Feasibility of Using Hardware Breakpoints To Extend the Race Window -… https://

    @ksg93rd

    6 Jan 2025

    511 Impressions

    3 Retweets

    6 Likes

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Configurations

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References

Sources include official advisories and independent security research.