A covert storage channel transfers information through the setting of bits by one program and the reading of those bits by another. What distinguishes this case from that of ordinary operation is that the bits are used to convey encoded information.
Covert storage channels occur when out-of-band data is stored in messages for the purpose of memory reuse. Covert channels are frequently classified as either storage or timing channels. Examples would include using a file intended to hold only audit information to convey user passwords--using the name of a file or perhaps status bits associated with it that can be read by all users to signal the contents of the file. Steganography, concealing information in such a manner that no one but the intended recipient knows of the existence of the message, is a good example of a covert storage channel.

Resultant

Implementation

High

Confidentiality
Read Application Data
Covert storage channels may provide attackers with important information about the system in question.

Integrity
Confidentiality
Read Application Data
If these messages or packets are sent with unnecessary data contained within, it may tip off malicious listeners as to the process that created the message. With this information, attackers may learn any number of things, including the hardware platform, operating system, or algorithms used by the sender. This information can be of significant value to the user in launching further attacks.

Implementation
Ensure that all reserved fields are set to zero before messages are sent and that no unnecessary information is included.

An excellent example of covert storage channels in a well known application is the ICMP error message echoing functionality. Due to ambiguities in the ICMP RFC, many IP implementations use the memory within the packet for storage or calculation. For this reason, certain fields of certain packets -- such as ICMP error packets which echo back parts of received messages -- may contain flaws or extra information which betrays information about the identity of the target operating system. This information is then used to build up evidence to decide the environment of the target. This is the first crucial step in determining if a given system is vulnerable to a particular flaw and what changes must be made to malicious code to mount a successful attack.

Storage

Covert storage channel

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

As of CWE 4.9, members of the CWE Hardware SIG are working to improve CWE's coverage of transient execution weaknesses, which include issues related to Spectre, Meltdown, and other attacks that create or exploit covert channels. As a result of that work, this entry might change in CWE 4.10.

Landwehr
2006-07-19
Draft 3
2006-07-19

Eric Dalci
Cigital
2008-07-01
updated Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings

CWE Content Team
MITRE
2008-10-14
updated Description

CWE Content Team
MITRE
2009-07-27
updated Common_Consequences, Description

CWE Content Team
MITRE
2009-10-29
updated Other_Notes

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated Relationships

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2022-10-13
updated Maintenance_Notes

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2024-07-16
4.15
2024-07-16
updated References

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Weakness_Ordinalities