CVE-2021-46988

MEDIUMNVD 5.55.5—

5.5

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

userfaultfd: release page in error path to avoid BUG_ON

Consider the following sequence of events:

Userspace issues a UFFD ioctl, which ends up calling into

shmem_mfill_atomic_pte(). We successfully account the blocks, we shmem_alloc_page(), but then the copy_from_user() fails. We return -ENOENT. We don't release the page we allocated.

Our caller detects this error code, tries the copy_from_user() after

dropping the mmap_lock, and retries, calling back into shmem_mfill_atomic_pte().

Meanwhile, let's say another process filled up the tmpfs being used.
So shmem_mfill_atomic_pte() fails to account blocks this time, and

immediately returns - without releasing the page.

This triggers a BUG_ON in our caller, which asserts that the page should always be consumed, unless -ENOENT is returned.

To fix this, detect if we have such a "dangling" page when accounting fails, and if so, release it before returning.

CVSS v3: 5.5
EG Score: 5.5(medium)
EPSS: 14.8%
KEV: Not listed

Published

February 28, 2024

Last Modified

December 26, 2024

References (14)

416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744de
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171c
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744de
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171c
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43

Weakness Classification(1)

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

CWE-416Use After Free

Data Freshness Timeline

(refreshed 12× in last 7d / 48× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. 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. Most recent first.

2026-06-21 01:58 UTCEPSS rescore
2026-06-21 01:58 UTCEPSS rescore
2026-06-19 19:24 UTCEPSS rescore
2026-06-19 19:24 UTCEPSS rescore
2026-06-18 17:51 UTCEPSS rescore
2026-06-18 17:51 UTCEPSS rescore
2026-06-17 17:51 UTCEPSS rescore
2026-06-17 17:51 UTCEPSS rescore
2026-06-16 17:51 UTCEPSS rescore
2026-06-15 17:46 UTCEPSS rescore
2026-06-14 23:15 UTCEPSS rescore
2026-06-14 23:15 UTCEPSS rescore
2026-06-12 23:10 UTCEPSS rescore
2026-06-11 13:58 UTCEPSS rescore
2026-06-10 22:16 UTCEPSS rescore
2026-06-10 13:20 UTCEPSS rescore
2026-06-09 04:00 UTCOSV refresh
2026-06-08 14:15 UTCEPSS rescore
2026-06-08 14:15 UTCEPSS rescore
2026-06-08 14:15 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-06 13:46 UTCEPSS rescore
2026-06-06 13:46 UTCEPSS rescore
2026-06-05 22:45 UTCEPSS rescore

Show 23 more

2026-06-05 22:45 UTCEPSS rescore
2026-06-05 06:09 UTCEPSS rescore
2026-06-05 06:09 UTCEPSS rescore
2026-06-04 13:11 UTCEPSS rescore
2026-06-04 13:10 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-01 13:50 UTCEPSS rescore
2026-06-01 13:50 UTCEPSS rescore
2026-05-31 22:29 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore
2026-05-29 13:42 UTCEPSS rescore
2026-05-28 13:43 UTCEPSS rescore
2026-05-28 13:43 UTCEPSS rescore
2026-05-27 13:39 UTCEPSS rescore
2026-05-27 13:39 UTCEPSS rescore
2026-05-26 13:43 UTCEPSS rescore
2026-05-26 13:42 UTCEPSS rescore
2026-05-26 07:17 UTCEPSS rescore
2026-05-26 07:17 UTCEPSS rescore
2026-05-24 07:44 UTCEG score recompute
2026-05-24 07:44 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2021-46988?

CVE-2021-46988 is a medium vulnerability published on February 28, 2024. In the Linux kernel, the following vulnerability has been resolved: userfaultfd: release page in error path to avoid BUG_ON Consider the following sequence of events: 1. Userspace issues a UFFD ioctl, which ends up calling into shmemmfillatomic_pte(). We successfully account the blocks, we…

When was CVE-2021-46988 disclosed?

CVE-2021-46988 was first published in the National Vulnerability Database on February 28, 2024, with the most recent update on December 26, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-46988 actively exploited?

CVE-2021-46988 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 14.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-46988?

CVE-2021-46988 has a CVSS v3 base score of 5.5 (NVD).

How do I remediate CVE-2021-46988?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-46988, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2021-46988

Explore →

Is Your Infrastructure Affected by CVE-2021-46988?

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

Start Free Scan →Browse All CVEs

CVE-2021-46988

📅 Published

🔄 Last Modified

🔗 References (14)

Weakness Classification(1)

Data Freshness Timeline

❓ Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-46988?

🔗 Related CVEs(same CWE)

Same CWE

Published

Last Modified

References (14)

Frequently asked(5)

Related CVEs(same CWE)