DaystoPatch

Linux kernelExploited incident

Linux kernel netfilter x_tables heap out-of-bounds write (CVE-2021-22555)

CVE-2021-22555High, CVSS 8.3In CISA's Known Exploited Vulnerabilities catalog since 6 Oct 2025

  • Exploited after a fix existed
FixedFixed for every supported version on the day it became public.

Response

Silence
not dated
First public report to first vendor statement
Exposure
0h
First public report to first fix
Follow-through
0h
First public report to a fix for every supported version
  • Vendor silent
  • Vendor statement, no fix
  • Fixed for some versions
  • Fixed when disclosed
  • Date only, no time of day

Timeline and evidence

Open a moment to see its source and archived quote.

  1. First public report

    CVE-2021-22555 record (CNA: Google)CuratedQuote verified

    "datePublished":"2021-07-07T11:20:10.668Z"

    Published by Google's CNA with Google Security Research advisory GHSA-xxx5-8mvq-3528 (Andy Nguyen's write-up and exploit), about three months after the fix.

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    sha256:e20e610ab99fee6b…
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    4 more sources for this moment
    CVE.org record CVE-2021-22555ClaimedQuote verified7 Jul 2021, 11:20 UTC

    A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption)

    CVE record published.

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    Hacker NewsClaimedQuote not checked yet15 Jul 2021, 06:42 UTC

    CVE-2021-22555: Turning \x00\x00 into 10000$

    Earliest third-party post we hold.

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    Hacker News hn
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    Not checked yet
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    CISA KEV (CVE-2021-22555)ClaimedQuote verified6 Oct 2025

    Linux Kernel Heap Out-of-Bounds Write Vulnerability

    Added to CISA's KEV catalog on 2025-10-06.

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    Found in the archived copy
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    sha256:ef8fffede5c47200…
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    Bluesky postClaimedQuote not checked yet6 Oct 2025, 17:42 UTC

    CVE-2021-22555 Linux Kernel Heap Out-of-Bounds Write Vulnerability

    Earliest third-party post we hold.

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    Bluesky post social
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  2. Vendor statement

    No public statement from the vendor found yet.

  3. First workaround

    No official mitigation found yet.

  4. First fix

    at disclosure

    kernel.org ChangeLog-5.11.15CuratedQuote verified

    Date: Fri Apr 16 11:38:15 2021 +0200

    Top entry of the Linux 5.11.15 ChangeLog is the release commit 'Linux 5.11.15' dated Fri Apr 16 11:38:15 2021 +0200 = 2021-04-16 09:38 UTC (commit author date). Stable backports 5.11.15, 5.10.31, 5.4.113, 4.19.188, 4.14.231, 4.9.267 and 4.4.267 were all tagged on 2021-04-16; mainline 5.12 followed.

    Source
    kernel.org ChangeLog-5.11.15 vendor github
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  5. Fixed for all versions

    at disclosure

    kernel.org ChangeLog-4.4.267CuratedQuote verified

    Date: Fri Apr 16 12:00:23 2021 +0200

    Top entry of the Linux 4.4.267 ChangeLog is the release commit 'Linux 4.4.267' dated Fri Apr 16 12:00:23 2021 +0200 = 2021-04-16 10:00 UTC (commit author date). Last of the 2021-04-16 stable releases.

    Source
    kernel.org ChangeLog-4.4.267 vendor github
    Recorded time
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    Curated. Found by a researcher, with a verbatim quote and link.
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    Found in the archived copy
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    sha256:64322a1e8d39edf3…
    Used in metrics
    Yes
    Dispute this timestamp

Send this to your boss

No brief for this incident yet. We write one for every open incident and every critical bug exploited before a fix.

Affected products

  • Linux kernel 2.6.19 up to 4.4.266, 4.9.266, 4.14.230, 4.19.187, 5.4.112, 5.10.30, 5.11.14 (net/netfilter/x_tables.c)
How we built this timeline

Coordinated disclosure: fixed upstream in April 2021 (commit b29c457a6511 'netfilter: x_tables: fix compat match/target pad out-of-bound write'), disclosed publicly 7 Jul 2021, KEV-listed 6 Oct 2025. No Vendor statement moment is recorded: before the kernel became a CNA (2024) the upstream kernel published no security advisories, and the fixing releases do not describe the bug as a vulnerability.

Fixed-version mapping per branch is from the linuxkernelcves.com dataset (raw.githubusercontent.com/nluedtke/linux_kernel_cves data/stream_fixes.json) and NVD's CPE ranges; release dates are from the kernel.org ChangeLog files (git.kernel.org tag pages were used before the 23 Oct 2026 correction pass; robots.txt blocks them). No report of exploitation before the fix.

CVSS 8.3 from the Google CNA record (NVD: 7.8).

Related

No related incidents.

Linux kernel report card