5 Medium
CVSS3
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
LOW
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
6 Medium
CVSS2
Access Vector
NETWORK
Access Complexity
MEDIUM
Authentication
SINGLE
Confidentiality Impact
PARTIAL
Integrity Impact
PARTIAL
Availability Impact
PARTIAL
AV:N/AC:M/Au:S/C:P/I:P/A:P
0.008 Low
EPSS
Percentile
81.6%
In runc, netlink is used internally as a serialization system for specifying the relevant container configuration to the C portion of our 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.
Prior to 9c444070ec7bb83995dbc0185da68284da71c554, in practice it was fairly difficult to specify an arbitrary-length netlink message with most container runtimes. The only user-controlled byte array was the namespace paths attributes which can be specified in runcโs config.json
, but as far as we can tell no container runtime gives raw access to that configuration setting โ and having raw access to that setting would allow the attacker to disable namespace protections entirely anyway (setting them to /proc/1/ns/...
for instance). In addition, each namespace path is limited to 4096 bytes (with only 7 namespaces supported by runc at the moment) meaning that even with custom namespace paths it appears an attacker still cannot shove enough bytes into the netlink bytemsg in order to overflow the uint16 counter.
However, out of an abundance of caution (given how old this bug is) we decided to treat it as a potentially exploitable vulnerability with a low severity. After 9c444070ec7bb83995dbc0185da68284da71c554 (which was not present in any release of runc prior to the discovery of this bug), all mount paths are included as a giant netlink message which means that this bug becomes significantly more exploitable in more reasonable threat scenarios.
The main users impacted are those who allow untrusted images with untrusted configurations to run on their machines (such as with shared cloud infrastructure), though as mentioned above it appears this bug was not practically exploitable on any released version of runc to date.
The patch for this is d72d057ba794164c3cce9451a00b72a78b25e1ae and runc 1.0.3 was released with this bug fixed.
To the extent this is exploitable, disallowing untrusted namespace paths in container configuration should eliminate all practical ways of exploiting this bug. It should be noted that untrusted namespace paths would allow the attacker to disable namespace protections entirely even in the absence of this bug.
Thanks to Felix Wilhelm from Google Project Zero for discovering and reporting this vulnerability. In particular, the fact they found this vulnerability so quickly, before we made a 1.1 release of runc (which wouldโve been vulnerable) was quite impressive.
If you have any questions or comments about this advisory:
CPE | Name | Operator | Version |
---|---|---|---|
github.com/opencontainers/runc | lt | 1.0.3 |
bugs.chromium.org/p/project-zero/issues/detail?id=2241
github.com/opencontainers/runc
github.com/opencontainers/runc/commit/9c444070ec7bb83995dbc0185da68284da71c554
github.com/opencontainers/runc/commit/d72d057ba794164c3cce9451a00b72a78b25e1ae
github.com/opencontainers/runc/commit/dde509df4e28cec33b3c99c6cda3d4fd5beafc77
github.com/opencontainers/runc/commit/f50369af4b571e358f20b139eea52d612eb55eed
github.com/opencontainers/runc/security/advisories/GHSA-v95c-p5hm-xq8f
lists.debian.org/debian-lts-announce/2021/12/msg00005.html
lists.debian.org/debian-lts-announce/2024/02/msg00005.html
nvd.nist.gov/vuln/detail/CVE-2021-43784
pkg.go.dev/vuln/GO-2022-0274
5 Medium
CVSS3
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
LOW
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
6 Medium
CVSS2
Access Vector
NETWORK
Access Complexity
MEDIUM
Authentication
SINGLE
Confidentiality Impact
PARTIAL
Integrity Impact
PARTIAL
Availability Impact
PARTIAL
AV:N/AC:M/Au:S/C:P/I:P/A:P
0.008 Low
EPSS
Percentile
81.6%