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CVE Record

CVE-2023-53727: net/sched: fq_pie: avoid stalls in fq_pie_timer()

In the Linux kernel, the following vulnerability has been resolved: net/sched: fq_pie: avoid stalls in fq_pie_timer() When setting a high number of flows (limit being 65536), fq_pie_timer() is currently using too much time as syzbot reported. Add logic to yield the cpu every 2048 flows (less than 150 usec on debug kernels). It should also help by not blocking qdisc fast paths for too long. Worst case (65536 flows) would need 31 jiffies for a complete scan. Relevant extract from syzbot report: rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2663 jiffies s: 873 root: 0x1/. rcu: blocking rcu_node structures (internal RCU debug): Sending NMI from CPU 1 to CPUs 0: NMI backtrace for cpu 0 CPU: 0 PID: 5177 Comm: syz-executor273 Not tainted 6.5.0-syzkaller-00453-g727dbda16b83 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023 RIP: 0010:check_kcov_mode kernel/kcov.c:173 [inline] RIP: 0010:write_comp_data+0x21/0x90 kernel/kcov.c:236 Code: 2e 0f 1f 84 00 00 00 00 00 65 8b 05 01 b2 7d 7e 49 89 f1 89 c6 49 89 d2 81 e6 00 01 00 00 49 89 f8 65 48 8b 14 25 80 b9 03 00 <a9> 00 01 ff 00 74 0e 85 f6 74 59 8b 82 04 16 00 00 85 c0 74 4f 8b RSP: 0018:ffffc90000007bb8 EFLAGS: 00000206 RAX: 0000000000000101 RBX: ffffc9000dc0d140 RCX: ffffffff885893b0 RDX: ffff88807c075940 RSI: 0000000000000100 RDI: 0000000000000001 RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffffc9000dc0d178 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 FS: 0000555555d54380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f6b442f6130 CR3: 000000006fe1c000 CR4: 00000000003506f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <NMI> </NMI> <IRQ> pie_calculate_probability+0x480/0x850 net/sched/sch_pie.c:415 fq_pie_timer+0x1da/0x4f0 net/sched/sch_fq_pie.c:387 call_timer_fn+0x1a0/0x580 kernel/time/timer.c:1700

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2023-53727 is a Linux kernel scheduling issue in fq_pie traffic control. With a very high flow count, a timer scan can monopolize CPU long enough to trigger RCU stall warnings and slow networking paths. The source bundle does not provide a CVSS score or evidence of active exploitation.

Executive priority

Prioritize patching on network-heavy Linux hosts, appliances, gateways, and multi-tenant systems using traffic shaping. This does not currently look like an emergency internet-wide exploit, but it can affect availability where the vulnerable scheduler is active.

Technical view

The flaw is in net/sched sch_fq_pie. fq_pie_timer() could spend excessive time scanning up to 65,536 flows, causing expedited RCU stalls and blocking qdisc fast paths. The kernel fix adds periodic CPU yielding every 2,048 flows to reduce long uninterrupted timer execution.

Likely exposure

Exposure is most likely on Linux systems running affected kernel versions with fq_pie traffic shaping enabled, especially configurations allowing high flow limits. The bundle lists Linux 5.6, 5.10.195, 5.15.132, 6.1.54, 6.5.4, and 6.6 as affected version markers, but distro backports must be checked.

Exploitation context

The provided sources show syzbot-triggered kernel stalls, not confirmed real-world exploitation. The CVE is not marked KEV in the bundle. Treat it as a potential local or configuration-dependent denial-of-service risk unless vendor guidance states otherwise.

Researcher notes

Evidence is limited to the CVE description and kernel stable references. The root condition is excessive timer work across many fq_pie flows. No exploit prerequisites, privilege requirements, or distro-specific fixed package versions are provided in the bundle.

Mitigation direction

  • Apply a vendor kernel update containing the stable fq_pie_timer() fix.
  • Check Linux distribution advisories for backported fixes before judging by version alone.
  • Avoid high-flow fq_pie configurations until patched, where operationally acceptable.
  • Monitor kernel logs for RCU stalls involving fq_pie_timer or sch_fq_pie.

Validation and detection

  • Inventory Linux kernels and compare against vendor-fixed package versions.
  • Identify systems using fq_pie qdisc in traffic control configurations.
  • Review fq_pie flow-limit settings on exposed or multi-tenant hosts.
  • Confirm the deployed kernel includes the referenced stable commits or vendor equivalent.
Prepared
Confidence
medium
Sources
7

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

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CVE-2023-53727 mapping review

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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
0ADP providers
6Source links

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.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxec97ecf1ebe485a17cd8395a5f35e6b80b57665a, ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, ec97ecf1ebe485a17cd8395a5f35e6b80b57665aunaffected
LinuxLinux5.6, 0, 5.10.195, 5.15.132, 6.1.54, 6.5.4, 6.6affected
Weakness

CWE details

No CWE listed

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