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NVD / CVE Program· CNA Linux

CVE-2021-47185: tty: tty_buffer: Fix the softlockup issue in flush_to_ldisc

Noroxi assessment

Priority: Monitor (action score 17/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.17% (FIRST EPSS).
  • Someone with local access to the system can trigger it. Administrator privileges are required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 0380f643f3a7a61b0845cdc738959c2ad5735d61, 3968ddcf05fb4b9409cd1859feb06a5b0550a1c1, 4c1623651a0936ee197859824cdae6ebbd04d3ed.
  • Mentioned 2 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 0380f643f3a7a61b0845cdc738959c2ad5735d61, 3968ddcf05fb4b9409cd1859feb06a5b0550a1c1, 4c1623651a0936ee197859824cdae6ebbd04d3ed or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: tty: tty_buffer: Fix the softlockup issue in flush_to_ldisc When running ltp testcase(ltp/testcases/kernel/pty/pty04.c) with arm64, there is a soft lockup, which look like this one: Workqueue: events_unbound flush_to_ldisc Call trace: dump_backtrace+0x0/0x1ec show_stack+0x24/0x30 dump_stack+0xd0/0x128 panic+0x15c/0x374 watchdog_timer_fn+0x2b8/0x304 __run_hrtimer+0x88/0x2c0 __hrtimer_run_queues+0xa4/0x120 hrtimer_interrupt+0xfc/0x270 arch_timer_handler_phys+0x40/0x50 handle_percpu_devid_irq+0x94/0x220 __handle_domain_irq+0x88/0xf0 gic_handle_irq+0x84/0xfc el1_irq+0xc8/0x180 slip_unesc+0x80/0x214 [slip] tty_ldisc_receive_buf+0x64/0x80 tty_port_default_receive_buf+0x50/0x90 flush_to_ldisc+0xbc/0x110 process_one_work+0x1d4/0x4b0 worker_thread+0x180/0x430 kthread+0x11c/0x120 In the testcase pty04, The first process call the write syscall to send data to the pty master. At the same time, the workqueue will do the flush_to_ldisc to pop data in a loop until there is no more data left. When the sender and workqueue running in different core, the sender sends data fastly in full time which will result in workqueue doing work in loop for a long time and occuring softlockup in flush_to_ldisc with kernel configured without preempt. So I add need_resched check and cond_resched in the flush_to_ldisc loop to avoid it.

MediumCVSS 4.4 · v3.1—No exploit Fix available
Published
Apr 10, 2024
Updated
Jun 17, 2026
EPSS
0.1% · 7th percentile

Report tools

JSON

Action score

17

Monitor

Low priority for now.

CVSS
17 / 40 · 4.4 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernelbefore 4.4.293
  • linux linux kernel4.5 and later · before 4.9.291
  • linux linux kernel4.10 and later · before 4.14.256
  • linux linux kernel4.15 and later · before 4.19.218
  • linux linux kernel4.20 and later · before 5.4.162
  • linux linux kernel5.5 and later · before 5.10.82
  • linux linux kernel5.11 and later · before 5.15.5

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 3.0affected
    • 81de916f19cf5f1437c0b9ed817364f0f7c81961 and later · before 0380f643f3a7a61b0845cdc738959c2ad5735d61affected · git
    • 81de916f19cf5f1437c0b9ed817364f0f7c81961 and later · before b1ffc16ec05ae40d82b6e373322d62e9d6b54fbcaffected · git
    • 81de916f19cf5f1437c0b9ed817364f0f7c81961 and later · before 4c1623651a0936ee197859824cdae6ebbd04d3edaffected · git
    • 81de916f19cf5f1437c0b9ed817364f0f7c81961 and later · before 4f300f47dbcf9c3d4b2ea76c8554c8f360400725affected · git
    • 81de916f19cf5f1437c0b9ed817364f0f7c81961 and later · before d491c84df5c469dd9621863b6a770b3428137063affected · git
    • 81de916f19cf5f1437c0b9ed817364f0f7c81961 and later · before 77e9fed33056f2a88eba9dd4d2d5412f0c7d1f41affected · git
    • 81de916f19cf5f1437c0b9ed817364f0f7c81961 and later · before 5c34486f04700f1ba04907231dce0cc2705c2d7daffected · git
    • 81de916f19cf5f1437c0b9ed817364f0f7c81961 and later · before 3968ddcf05fb4b9409cd1859feb06a5b0550a1c1affected · git
    • before 3.0not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:8bpftoolbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernelbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-abi-stablelistsbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-corebefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-cross-headersbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-debugbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-debug-corebefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-debug-develbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-debug-modulesbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-debug-modules-extrabefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-develbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-docbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-headersbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-modulesbefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-modules-extrabefore 4.18.0-553.5.1.el8_104.18.0-553.5.1.el8_10
AlmaLinux:8kernel-rtbefore 4.18.0-553.5.1.rt7.346.el8_104.18.0-553.5.1.rt7.346.el8_10
AlmaLinux:8kernel-rt-corebefore 4.18.0-553.5.1.rt7.346.el8_104.18.0-553.5.1.rt7.346.el8_10
AlmaLinux:8kernel-rt-debugbefore 4.18.0-553.5.1.rt7.346.el8_104.18.0-553.5.1.rt7.346.el8_10
AlmaLinux:8kernel-rt-debug-corebefore 4.18.0-553.5.1.rt7.346.el8_104.18.0-553.5.1.rt7.346.el8_10
AlmaLinux:8kernel-rt-debug-develbefore 4.18.0-553.5.1.rt7.346.el8_104.18.0-553.5.1.rt7.346.el8_10
AlmaLinux:8kernel-rt-debug-kvmbefore 4.18.0-553.5.1.rt7.346.el8_104.18.0-553.5.1.rt7.346.el8_10
AlmaLinux:8kernel-rt-debug-modulesbefore 4.18.0-553.5.1.rt7.346.el8_104.18.0-553.5.1.rt7.346.el8_10
AlmaLinux:8kernel-rt-debug-modules-extrabefore 4.18.0-553.5.1.rt7.346.el8_104.18.0-553.5.1.rt7.346.el8_10
AlmaLinux:8kernel-rt-develbefore 4.18.0-553.5.1.rt7.346.el8_104.18.0-553.5.1.rt7.346.el8_10

+96

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2021-47183Apr 10, 2024 · scsi: lpfc: Fix link down processing to address NULL pointer dereference
    22Monitor
  • ← EarlierCVE-2021-47184Apr 10, 2024 · i40e: Fix NULL ptr dereference on VSI filter sync
    22Monitor
  • Later →CVE-2021-47186Apr 10, 2024 · tipc: check for null after calling kmemdup
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux0380f643f3a7a61b0845cdc738959c2ad5735d61Vendor (CNA)
Linux Linux3968ddcf05fb4b9409cd1859feb06a5b0550a1c1Vendor (CNA)
Linux Linux4c1623651a0936ee197859824cdae6ebbd04d3edVendor (CNA)
Linux Linux4f300f47dbcf9c3d4b2ea76c8554c8f360400725Vendor (CNA)
Linux Linux5c34486f04700f1ba04907231dce0cc2705c2d7dVendor (CNA)
Linux Linux77e9fed33056f2a88eba9dd4d2d5412f0c7d1f41Vendor (CNA)
Linux Linuxb1ffc16ec05ae40d82b6e373322d62e9d6b54fbcVendor (CNA)
Linux Linuxd491c84df5c469dd9621863b6a770b3428137063Vendor (CNA)
almalinux:bpftool4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-abi-stablelists4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-core4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-cross-headers4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-debug4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-debug-core4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-debug-devel4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-debug-modules4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-debug-modules-extra4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-devel4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
almalinux:kernel-doc4.18.0-553.5.1.el8_10 · AlmaLinux:8Package registry (OSV)
debian:linux5.15.5-1 · Debian:12Package registry (OSV)
opensuse:dtb-aarch645.14.21-150500.55.62.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-64kb5.14.21-150500.55.62.2 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-azure5.14.21-150500.33.51.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-debug5.14.21-150500.55.62.2 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-default5.14.21-150400.24.119.1 · openSUSE:Leap Micro 5.3Package registry (OSV)
opensuse:kernel-default-base5.14.21-150400.24.119.1.150400.24.56.1 · openSUSE:Leap Micro 5.3Package registry (OSV)
opensuse:kernel-docs5.14.21-150500.55.62.2 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-kvmsmall5.14.21-150500.55.62.2 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-obs-build5.14.21-150500.55.62.2 · openSUSE:Leap 15.5Package registry (OSV)

+29

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • Administrator privileges are required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
High
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-667 · Improper Locking

CVSS vector

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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records