CVE-2021-47527

Serial I/O hang via uncleared transmit buffer

Published May 24, 2024 · Updated May 11, 2026

A transmit-buffer lifetime flaw in affected Linux kernel releases allows local users to hang serial I/O or transmit stale buffered data. The serial core fails to free and clear its transmit buffer on final close, so a reopened port can retain stale bytes and an opened port leaks its buffer when the driver is unbound. Exploitation requires local access to an affected serial port; consequences are an indefinitely waiting drain ioctl, stale transmission, or an unbind-time memory leak.

CVSS severity5.5
Medium
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A transmit-buffer lifetime flaw in affected Linux kernel releases allows local users to hang serial I/O or transmit stale buffered data. The serial core fails to free and clear its transmit buffer on final close, so a reopened port can retain stale bytes and an opened port leaks its buffer when the driver is unbound. Exploitation requires local access to an affected serial port; consequences are an indefinitely waiting drain ioctl, stale transmission, or an unbind-time memory leak.

The record

CVE
CVE-2021-47527
Published
May 24, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-401, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 24, 2024CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.9
  2. Affected versionversion=761ed4a94582ab291aa24dcbea4e01e8936488c8 <00de977f9e0aa9760d9a79d1e41ff780f74e3424
  3. Affected versionversion=761ed4a94582ab291aa24dcbea4e01e8936488c8 <011f6c92b5bf6e1fbfdedc8b5232f64c1c493206
  4. Affected versionversion=761ed4a94582ab291aa24dcbea4e01e8936488c8 <1179b168fa3f3a6aae3bd140000455a0e58457db
  5. Affected versionversion=761ed4a94582ab291aa24dcbea4e01e8936488c8 <64e491c1634b73d3bddc081d08620bdc92ab2c12
  6. Affected versionversion=761ed4a94582ab291aa24dcbea4e01e8936488c8 <c5da8aa441053958594f94254592bb41264bdfbf
  7. Affected versionversion=761ed4a94582ab291aa24dcbea4e01e8936488c8 <e1722acf4f0d4d67b60f57e08ce16f8b66cd4b8f
  8. Affected versionversion=761ed4a94582ab291aa24dcbea4e01e8936488c8 <e74d9663fd57640fc3394abb5c76fa95b9cc2f2e

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.9; version=761ed4a94582ab291aa24dcbea4e01e8936488c8 <00de977f9e0aa9760d9a79d1e41ff780f74e3424; version=761ed4a94582ab291aa24dcbea4e01e8936488c8 <011f6c92b5bf6e1fbfdedc8b5232f64c1c493206; version=761ed4a94582ab291aa24dcbea4e01e8936488c8 <1179b168fa3f3a6aae3bd140000455a0e58457db; version=761ed4a94582ab291aa24dcbea4e01e8936488c8 <64e491c1634b73d3bddc081d08620bdc92ab2c12; version=761ed4a94582ab291aa24dcbea4e01e8936488c8 <c5da8aa441053958594f94254592bb41264bdfbf; version=761ed4a94582ab291aa24dcbea4e01e8936488c8 <e1722acf4f0d4d67b60f57e08ce16f8b66cd4b8f; version=761ed4a94582ab291aa24dcbea4e01e8936488c8 <e74d9663fd57640fc3394abb5c76fa95b9cc2f2e

Published CVSS scores

5.5SUSECVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5Amazon LinuxCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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