CVE-2022-38150
Description
A flaw was found in Varnish where a denial of service attack can be performed against Varnish Cache servers by specially formatting the reason phrase of the backend response status line. To execute an attack, the attacker needs the ability to influence the HTTP/1 responses that the Varnish Server receives from its configured backends, causing the Varnish Server to assert and automatically restart.
Mitigation
As mentioned in the upstream security advisory, If upgrading Varnish is not possible, it is possible to mitigate the problem by adding the following snippet at the beginning of the vcl_backend_response VCL function:
sub vcl_backend_response {
set beresp.status = beresp.status;
}
By setting the status code to itself as described above, the reason field will automatically be reset to the standard value for the given status code, or “Unknown HTTP Status” if no standard value exists for that code. This would overwrite any existing attack content in the reason field.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | 7.5 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
An attacker could provide unexpected values and cause a program crash or arbitrary control of resource allocation, leading to excessive consumption of resources such as memory and CPU.
Confidentiality
Technical Impact: Read Memory; Read Files or Directories
An attacker could read confidential data if they are able to control resource references.
Integrity,Confidentiality,Availability
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
An attacker could use malicious input to modify data or possibly alter control flow in unexpected ways, including arbitrary command execution.
Acknowledgements
Upstream acknowledges Anthony Schwartz as the original reporter.
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