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Linux KernelOperating system · Linux

CVE-2021-47245

HIGH · 7.1 CVSS v3.1 Published 2024-05-21
Fix available
A fix is available. Upgrade to 4.4.274 / 4.9.274 or later.
See remediation →
73/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: netfilter: synproxy: Fix out of bounds when parsing TCP options The TCP option parser in synproxy (synproxy_parse_options) could read one byte out of bounds. When the length is 1, the execution flow gets into the loop, reads one byte of the opcode, and if the opcode is neither TCPOPT_EOL nor TCPOPT_NOP, it reads one more byte, which exceeds the length of 1. This fix is inspired by commit 9609dad263f8 ("ipv4: tcp_input: fix stack out of bounds when parsing TCP options."). v2 changes: Added an early return when length < 0 to avoid calling skb_header_pointer with negative length.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-125

The code reads past the end (or before the start) of a buffer, returning memory that was never meant to be exposed. Attackers use it to leak secrets like keys or to defeat memory-protection defences. Remediation is validating indices and lengths before every read.

General guidance for the out-of-bounds read class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 3.12, < 4.4.274>= 4.5, < 4.9.274>= 4.10, < 4.14.238>= 4.15, < 4.19.196>= 4.20, < 5.4.128>= 5.5, < 5.10.46>= 5.11, < 5.12.13= 5.13

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.4.274 / 4.9.274 / 4.14.238 or later
Fixed in 4.4.2744.9.2744.14.238
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux kernel 4.4.274, 4.9.274, 4.14.238, or 4.19.196 (depending on your branch)

  1. Check the currently running kernel version using `uname -r` or `cat /proc/version`
  2. Identify which major kernel branch your version belongs to (e.g., 4.4.x, 4.9.x, 4.14.x, or 4.19.x)
  3. Upgrade the Linux kernel to a version that includes the fix: for 4.4.x series upgrade to 4.4.274 or later; for 4.9.x series upgrade to 4.9.274 or later; for 4.14.x series upgrade to 4.14.238 or later; for 4.19.x series upgrade to 4.19.196 or later
  4. After kernel upgrade, reboot the system to load the fixed kernel
  5. Verify the system is running the patched kernel using `uname -r`
Caveat Kernel upgrades may require rebuild of out-of-tree kernel modules; ensure compatibility of hardware drivers and critical modules with the new kernel version before rebooting

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,200. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-47245 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data