CVE-2021-47557

MEDIUMNVD 5.55.5

Also known asEUVD-2021-34559 (ENISA EUVD)Source: ENISA EUVD

5.5EG

EchelonGraph verdictMonitorRemediate within your standard update timelines (the SSVC decision on this page).

Lower severity and no public exploit yet

CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 5.5Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

In the Linux kernel, the following vulnerability has been resolved:

net/sched: sch_ets: don't peek at classes beyond 'nbands'

when the number of DRR classes decreases, the round-robin active list can contain elements that have already been freed in ets_qdisc_change(). As a consequence, it's possible to see a NULL dereference crash, caused by the attempt to call cl->qdisc->ops->peek(cl->qdisc) when cl->qdisc is NULL:

BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 1 PID: 910 Comm: mausezahn Not tainted 5.16.0-rc1+ #475 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014 RIP: 0010:ets_qdisc_dequeue+0x129/0x2c0 [sch_ets] Code: c5 01 41 39 ad e4 02 00 00 0f 87 18 ff ff ff 49 8b 85 c0 02 00 00 49 39 c4 0f 84 ba 00 00 00 49 8b ad c0 02 00 00 48 8b 7d 10 <48> 8b 47 18 48 8b 40 38 0f ae e8 ff d0 48 89 c3 48 85 c0 0f 84 9d RSP: 0000:ffffbb36c0b5fdd8 EFLAGS: 00010287 RAX: ffff956678efed30 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000002 RSI: ffffffff9b938dc9 RDI: 0000000000000000 RBP: ffff956678efed30 R08: e2f3207fe360129c R09: 0000000000000000 R10: 0000000000000001 R11: 0000000000000001 R12: ffff956678efeac0 R13: ffff956678efe800 R14: ffff956611545000 R15: ffff95667ac8f100 FS: 00007f2aa9120740(0000) GS:ffff95667b800000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000018 CR3: 000000011070c000 CR4: 0000000000350ee0 Call Trace: qdisc_peek_dequeued+0x29/0x70 [sch_ets] tbf_dequeue+0x22/0x260 [sch_tbf] __qdisc_run+0x7f/0x630 net_tx_action+0x290/0x4c0 __do_softirq+0xee/0x4f8 irq_exit_rcu+0xf4/0x130 sysvec_apic_timer_interrupt+0x52/0xc0 asm_sysvec_apic_timer_interrupt+0x12/0x20 RIP: 0033:0x7f2aa7fc9ad4 Code: b9 ff ff 48 8b 54 24 18 48 83 c4 08 48 89 ee 48 89 df 5b 5d e9 ed fc ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 f3 0f 1e fa <53> 48 83 ec 10 48 8b 05 10 64 33 00 48 8b 00 48 85 c0 0f 85 84 00 RSP: 002b:00007ffe5d33fab8 EFLAGS: 00000202 RAX: 0000000000000002 RBX: 0000561f72c31460 RCX: 0000561f72c31720 RDX: 0000000000000002 RSI: 0000561f72c31722 RDI: 0000561f72c31720 RBP: 000000000000002a R08: 00007ffe5d33fa40 R09: 0000000000000014 R10: 0000000000000000 R11: 0000000000000246 R12: 0000561f7187e380 R13: 0000000000000000 R14: 0000000000000000 R15: 0000561f72c31460 Modules linked in: sch_ets sch_tbf dummy rfkill iTCO_wdt intel_rapl_msr iTCO_vendor_support intel_rapl_common joydev virtio_balloon lpc_ich i2c_i801 i2c_smbus pcspkr ip_tables xfs libcrc32c crct10dif_pclmul crc32_pclmul crc32c_intel ahci libahci ghash_clmulni_intel serio_raw libata virtio_blk virtio_console virtio_net net_failover failover sunrpc dm_mirror dm_region_hash dm_log dm_mod CR2: 0000000000000018

Ensuring that 'alist' was never zeroed [1] was not sufficient, we need to remove from the active list those elements that are no more SP nor DRR.

[1] https://lore.kernel.org/netdev/60d274838bf09777f0371253416e8af71360bc08.1633609148.git.dcaratti@redhat.com/

v3: fix race between ets_qdisc_change() and ets_qdisc_dequeue() delisting DRR classes beyond 'nbands' in ets_qdisc_change() with the qdisc lock acquired, thanks to Cong Wang.

v2: when a NULL qdisc is found in the DRR active list, try to dequeue skb from the next list item.

CVSS v3: 5.5
EG Score: 5.5MEDIUMmedium confidence
EG Risk: 25
EPSS PROB: 0.2%
EPSS %ILE: 15th
KEV: Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (5.5): severity, escalated by confirmed exploitation. This CVE's 5.5 is its impact severity (EG Severity), not escalated.

EG Severity: 5.5 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood: 0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-25). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation: None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority: SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

May 24, 2024

Last Modified

January 6, 2025

References (3)

CVE Programhttps://git.kernel.org/stable/c/ae2659d2c670252759ee9c823c4e039c0e05a6f2Patch
CVE Programhttps://git.kernel.org/stable/c/de6d25924c2a8c2988c6a385990cafbe742061bfPatch
CVE Programhttps://git.kernel.org/stable/c/e25bdbc7e951ae5728fee1f4c09485df113d013cPatch

Affected Packages

(4 across 4 ecosystems)

Debian:11(1)

Package	Vulnerable range	Fix by version range	Dependents
linux	5.10.46-4, 5.10.46-5, 5.10.70-1, 5.10.70-1~bpo10+1	every version up to 5.10.84-1: fixed in 5.10.84-1	—

Debian:12(1)

Package	Vulnerable range	Fix by version range	Dependents
linux	—	every version up to 5.15.15-1: fixed in 5.15.15-1	—

Debian:13(1)

Package	Vulnerable range	Fix by version range	Dependents
linux	—	every version up to 5.15.15-1: fixed in 5.15.15-1	—

Debian:14(1)

Package	Vulnerable range	Fix by version range	Dependents
linux	—	every version up to 5.15.15-1: fixed in 5.15.15-1	—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-476NULL Pointer Dereference

Data Freshness Timeline

(refreshed 7× in last 7d / 36× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 97 of 203 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 3 repeat rows among the latest 100 are merged into the row they repeat. The 106 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

2026-11-02 16:38 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-11-01 16:30 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-10-31 16:29 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-10-30 16:30 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-10-29 16:29 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-10-28 16:28 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-10-27 16:28 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-10-26 16:28 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-10-25 18:18 UTCEG score recompute
2026-10-25 16:29 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-10-24 21:41 UTCEG score recompute
2026-10-24 16:29 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-23 16:28 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-22 16:29 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-21 16:28 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-20 16:28 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-19 16:28 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-18 16:28 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-18 08:49 UTCEG score recompute
2026-10-17 16:29 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-16 16:34 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-15 16:28 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-14 16:29 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-13 16:28 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-12 19:05 UTCEG score recompute

Show 72 more

2026-10-12 16:30 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-11 23:31 UTCEG score recompute
2026-10-11 13:44 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-10 23:22 UTCOSV refresh
2026-10-10 19:56 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-09 20:04 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-10-08 16:40 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-10-07 23:45 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-10-06 15:14 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-10-05 17:40 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-10-04 23:19 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-10-03 14:22 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-10-02 16:23 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-09-30 15:45 UTCEG score recompute
2026-09-30 15:00 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-09-29 15:15 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-09-28 13:47 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-09-26 15:54 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-09-26 00:21 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-09-24 14:00 UTCEPSS rescoreEPSS 0.2% · 13th percentile
2026-09-23 13:45 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-22 14:44 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-21 20:28 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-21 11:49 UTCOSV refresh
2026-09-20 20:13 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-19 15:38 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-18 19:24 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-17 19:23 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-16 14:05 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-15 03:06 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-12 14:57 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-11 14:49 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-11 09:33 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-08 21:57 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-07 15:58 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-06 13:45 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-05 15:25 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-04 13:57 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-04 05:03 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-02 14:09 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-09-02 09:34 UTCOSV refresh
2026-09-01 13:51 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-30 19:14 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-30 01:19 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-28 21:38 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-27 14:22 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-26 14:43 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-25 13:46 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-08-24 14:13 UTCEPSS rescoreEPSS 0.2% · 14th percentile
2026-08-21 23:46 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-20 22:52 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-19 17:01 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-18 13:45 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-17 13:44 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-16 14:53 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-16 08:17 UTCOSV refresh
2026-08-16 02:11 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-15 01:27 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-13 21:57 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-12 13:48 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-11 13:38 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-09 13:44 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-08 16:34 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-07 16:24 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-05 19:15 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-04 15:06 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-04 10:34 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-03 10:33 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-02 02:24 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-08-01 01:42 UTCOSV refresh
2026-07-30 16:25 UTCEPSS rescoreEPSS 0.2% · 15th percentile
2026-07-30 01:28 UTCEPSS rescoreEPSS 0.2% · 15th percentile

Same CWE

10 shown

CWE-476

Frequently asked(5)

What is CVE-2021-47557?

CVE-2021-47557 is a medium-severity vulnerability; its CVE record was published on May 24, 2024. In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_ets: don't peek at classes beyond 'nbands' when the number of DRR classes decreases, the round-robin active list can contain elements that have already been freed in ets_qdisc_change(). As a consequence, it's…

When was the CVE record for CVE-2021-47557 published?

The CVE record for CVE-2021-47557 was published on May 24, 2024. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of January 6, 2025; the record at its source may have been updated since.

Is CVE-2021-47557 actively exploited?

CVE-2021-47557 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.2% probability of exploitation in the next 30 days (15th percentile of EPSS-scored CVEs).

What is the CVSS score of CVE-2021-47557?

CVE-2021-47557 has a CVSS v3 base score of 5.5 (NVD).

How do I remediate CVE-2021-47557?

A fix for CVE-2021-47557 is available: update to the fixed version the vendor names in its advisory.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-47557

Explore →

Is Your Infrastructure Affected by CVE-2021-47557?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Book a Demo →Browse All CVEs

CVE-2021-47557

📅 Published

🔄 Last Modified

🔗 References (3)