CVE-2021-40438

Known exploitThis CVE is high risk and there are known public exploits leveraging this vulnerability. Address this vulnerability with high priority.

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Last Modified: UTC

ImportantImportant ImpactWhat does this mean?
DescriptionStatementMitigationAdditional informationCVSS Score DetailsWeakness (CWE)FAQ

Description

A Server-Side Request Forgery (SSRF) flaw was found in mod_proxy of httpd. This flaw allows a remote, unauthenticated attacker to make the httpd server forward requests to an arbitrary server. The attacker could get, modify, or delete resources on other services that may be behind a firewall and inaccessible otherwise. The impact of this flaw varies based on what services and resources are available on the httpd network.

A Server-Side Request Forgery (SSRF) flaw was found in mod_proxy of httpd. This flaw allows a remote, unauthenticated attacker to make the httpd server forward requests to an arbitrary server. The attacker could get, modify, or delete resources on other services that may be behind a firewall and inaccessible otherwise. The impact of this flaw varies based on what services and resources are available on the httpd network.

Statement

Impact of the flaw set to Important because the actions an attacker can do varies a lot based on the kind of infrastructure in place, the kind of internal services and resources, and the available endpoints on those services. The attacker should also perform some kind of target-specific reconnaissance in order to find out all the above information. The version of httpd as shipped in Red Hat Enterprise Linux 7 is affected by this flaw even if the upstream code was not, because the Unix Domain Socket support required to trigger the flaw was backported. The version of httpd as shipped in Red hat Enterprise Linux 6 is not affected by this flaw because there is no support for Unix Domain Socket. The flaw can be triggered only if mod_proxy is in use (e.g. ProxyPass, ReverseProxy is used in the httpd configuration files).

Impact of the flaw set to Important because the actions an attacker can do varies a lot based on the kind of infrastructure in place, the kind of internal services and resources, and the available endpoints on those services. The attacker should also perform some kind of target-specific reconnaissance in order to find out all the above information.

The version of httpd as shipped in Red Hat Enterprise Linux 7 is affected by this flaw even if the upstream code was not, because the Unix Domain Socket support required to trigger the flaw was backported. The version of httpd as shipped in Red hat Enterprise Linux 6 is not affected by this flaw because there is no support for Unix Domain Socket.

The flaw can be triggered only if mod_proxy is in use (e.g. ProxyPass, ReverseProxy is used in the httpd configuration files).

Mitigation

Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.

Additional information

  • Bugzilla 2005117: httpd: mod_proxy: SSRF via a crafted request uri-path containing "unix:"
  • CWE-918: Server-Side Request Forgery (SSRF)
  • FAQ: Frequently asked questions about CVE-2021-40438

Common Vulnerability Scoring System (CVSS) Score Details

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).

CVSS v3 Score Breakdown
Red HatNVD

CVSS v3 Base Score

9

9

Attack Vector

Network

Network

Attack Complexity

High

High

Privileges Required

None

None

User Interaction

None

None

Scope

Changed

Changed

Confidentiality Impact

High

High

Integrity Impact

High

High

Availability Impact

High

High

CVSS v3 Vector

Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

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

Red Hat CVSS v3 Score Explanation

Scope set to Changed (S:C) because this flaw allows to perform requests on other services as if they would come from the httpd server, thus the real impact is to the data and services available elsewhere and not on the httpd server itself. Attack Complexity set to High (AC:H) because an attacker would need to first perform target-specific reconnaissance in order to find out the available services and their endpoints.

Scope set to Changed (S:C) because this flaw allows to perform requests on other services as if they would come from the httpd server, thus the real impact is to the data and services available elsewhere and not on the httpd server itself.

Attack Complexity set to High (AC:H) because an attacker would need to first perform target-specific reconnaissance in order to find out the available services and their endpoints.

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?

  • "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

What can I do if my product is listed as "Will not fix"?

A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
  • Apply a mitigation (if one exists).
  • Open a support case to request a prioritization of releasing a fix for this vulnerability.

What can I do if my product is listed as "Fix deferred"?

A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Apply a mitigation (if one exists).
  • Open a support case to request a prioritization of releasing a fix for this vulnerability.
  • Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

I have a Red Hat product but it is not in the above list, is it affected?

The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our Red Hat Vulnerability Scanner Certification program.

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