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Fencer Vulns
medium 5.5

CVE-2021-46935 json

binder: fix async_free_space accounting for empty parcels

published 2024-02-27 2 y ago modified 2026-06-17 4 mo ago also EUVD-2021-33583

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits
0
none known

Summary

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

binder: fix async_free_space accounting for empty parcels

In 4.13, commit 74310e06be4d ("android: binder: Move buffer out of area shared with user space") fixed a kernel structure visibility issue. As part of that patch, sizeof(void *) was used as the buffer size for 0-length data payloads so the driver could detect abusive clients sending 0-length asynchronous transactions to a server by enforcing limits on async_free_size.

Unfortunately, on the "free" side, the accounting of async_free_space did not add the sizeof(void *) back. The result was that up to 8-bytes of async_free_space were leaked on every async transaction of 8-bytes or less. These small transactions are uncommon, so this accounting issue has gone undetected for several years.

The fix is to use "buffer_size" (the allocated buffer size) instead of "size" (the logical buffer size) when updating the async_free_space during the free operation. These are the same except for this corner case of asynchronous transactions with payloads < 8 bytes.

Patch / fix

  • Linux Linux 4.14.261, 4.19.224, 5.4.170, 5.10.90, 5.15.13, 5.16
  • linux Debian 14, Debian 13, Debian 12 5.15.15-1

debian advisories DEBIAN-CVE-2021-46935

  • linux Ubuntu 18.04 LTS 4.15.0-173.182
  • linux Ubuntu 20.04 LTS 5.4.0-105.119
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1124.133
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1069.73
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1068.72
  • linux-ibm Ubuntu 20.04 LTS 5.4.0-1018.20
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1110.113
  • linux-kvm Ubuntu 20.04 LTS 5.4.0-1059.62

ubuntu advisories UBUNTU-CVE-2021-46935

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-46935 updated cvss 4.4

kernel: binder: fix async_free_space accounting for empty parcels

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-668 Exposure of Resource to Wrong Sphere
Technology feeds

References

Sources

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