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Debian LinuxOperating system · Debian

CVE-2021-43784

MEDIUM · 5.0 CVSS v3.1 Published 2021-12-06
Fix available
A fix is available. Upgrade to 1.0.3 or later.
See remediation →
56/100
Remediation priority · Elevated
Public exploit Remotely reachable 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
runc is a CLI tool for spawning and running containers on Linux according to the OCI specification. In runc, netlink is used internally as a serialization system for specifying the relevant container configuration to the `C` portion of the code (responsible for the based namespace setup of containers). In all versions of runc prior to 1.0.3, the encoder did not handle the possibility of an integer overflow in the 16-bit length field for the byte array attribute type, meaning that a large enough malicious byte array attribute could result in the length overflowing and the attribute contents being parsed as netlink messages for container configuration. This vulnerability requires the attacker to have some control over the configuration of the container and would allow the attacker to bypass the namespace restrictions of the container by simply adding their own netlink payload which disables all namespaces. The main users impacted are those who allow untrusted images with untrusted configurations to run on their machines (such as with shared cloud infrastructure). runc version 1.0.3 contains a fix for this bug. As a workaround, one may try disallowing untrusted namespace paths from your container. It should be noted that untrusted namespace paths would allow the attacker to disable namespace protections entirely even in the absence of this bug.

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-190

An arithmetic operation produces a value too large for its type and wraps around to an unexpected — often tiny or negative — number. That miscalculated value then drives a memory allocation or a bounds check, opening the door to corruption. The fix is checked arithmetic and validating sizes before they're used.

General guidance for the integer overflow 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
Debian LinuxOperating system
Affected:= 9.0
RuncApplication
Affected:< 1.0.3

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
Network
Complexity
High
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

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

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 1.0.3 or later
Fixed in 1.0.3
Vendor patch github.com →
Recommended fix High confidence

runc 1.0.3 or later

  1. 1. Identify the current version of runc installed on the system using `runc --version`
  2. 2. For Debian 9.0 systems, check if a patched version is available via `apt-cache policy runc`
  3. 3. If runc version is below 1.0.3, upgrade runc to version 1.0.3 or later using the appropriate package manager (e.g., `apt-get update && apt-get install runc` for Debian)
  4. 4. Alternatively, for manual installation, download runc v1.0.3 or later from the GitHub releases page: https://github.com/opencontainers/runc/releases
  5. 5. Verify the upgrade was successful by running `runc --version` and confirming the version is 1.0.3 or higher
  6. 6. Test that containers can still be created and run correctly after the upgrade

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 $2,850. 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-2021-43784 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
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  • Version or environment caveats, and links to real fixes
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