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AUSCERT External Security Bulletin Redistribution
ESB-2021.2097
Apache HTTP server security update
11 June 2021
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AusCERT Security Bulletin Summary
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Product: Apache HTTP Server
Publisher: Apache Software Foundation
Operating System: UNIX variants (UNIX, Linux, OSX)
Windows
Impact/Access: Denial of Service -- Remote/Unauthenticated
Access Confidential Data -- Remote/Unauthenticated
Reduced Security -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2021-31618 CVE-2021-30641 CVE-2021-26691
CVE-2021-26690 CVE-2020-35452 CVE-2020-13950
CVE-2020-13938 CVE-2019-17567
Original Bulletin:
https://httpd.apache.org/security/vulnerabilities_24.html
Comment: This bulletin contains eight (8) Apache Software Foundation security
advisories.
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CVE-2021-31618: NULL pointer dereference on specially crafted HTTP/2 request
Severity: important
Vendor: The Apache Software Foundation
Versions Affected:
2.4.47
httpd
Description:
Apache HTTP Server 2.4.47
Apache HTTP Server protocol handler for the HTTP/2 protocol checks received request headers against the
size limitations as configured for the server and used for the HTTP/1 protocol as well. On violation of
these restrictions and HTTP response is sent to the client with a status code indicating why the request
was rejected.
This rejection response was not fully initialised in the HTTP/2 protocol handler if the offending header
was the very first one received or appeared in a a footer. This led to a NULL pointer dereference on
initialised memory, crashing reliably the child process. Since such a triggering HTTP/2 request is easy
to craft and submit, this can be exploited to DoS the server.
This affected versions prior to 2.4.47
Mitigation:
none
Credit:
Apache HTTP server would like to thank LI ZHI XIN from NSFocus for reporting this.
References:
https://httpd.apache.org/security/vulnerabilities_24.html
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CVE-2021-30641: Unexpected URL matching with 'MergeSlashes OFF'
Severity: moderate
Vendor: The Apache Software Foundation
Versions Affected:
httpd 2.4.39 to 2.4.46
Description:
Apache HTTP Server 2.4.39 to 2.4.46
Unexpected matching behavior with 'MergeSlashes OFF'
Mitigation:
n/a
Credit:
Discovered by Christoph Anton Mitterer
References:
https://httpd.apache.org/security/vulnerabilities_24.html
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CVE-2021-26691: mod_session response handling heap overflow
Severity: low
Vendor: The Apache Software Foundation
Versions Affected:
httpd 2.4.0 to 2.4.46
Description:
Apache HTTP Server 2.4.0 to 2.4.46
A specially crafted SessionHeader sent by an origin server could cause a heap overflow
Mitigation:
None
Credit:
Discovered internally by Christophe Jaillet
References:
https://httpd.apache.org/security/vulnerabilities_24.html
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CVE-2021-26690: mod_session NULL pointer dereference
Severity: low
Vendor: The Apache Software Foundation
Versions Affected:
httpd 2.4.0 to 2.4.46
Description:
Apache HTTP Server 2.4.0 to 2.4.46
A specially crafted Cookie header handled by mod_session can cause a NULL pointer dereference
and crash, leading to a possible Denial Of Service
Mitigation:
None
Credit:
This issue was discovered and reported by GHSL team member @antonio-morales (Antonio Morales)
References:
https://httpd.apache.org/security/vulnerabilities_24.html
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CVE-2020-35452: mod_auth_digest possible stack overflow by one nul byte
Severity: low
Vendor: The Apache Software Foundation
Versions Affected:
httpd 2.4.0 to 2.4.46
Description:
Apache HTTP Server 2.4.0 to 2.4.46
A specially crafted Digest nonce can cause a stack overflow in mod_auth_digest. There is no report
of this overflow being exploitable, nor the Apache HTTP Server team could create one, though some
particular compiler and/or compilation option might make it possible, with limited consequences
anyway due to the size (a single byte) and the value (zero byte) of the overflow
Mitigation:
None
Credit:
This issue was discovered and reported by GHSL team member @antonio-morales (Antonio Morales)
References:
https://httpd.apache.org/security/vulnerabilities_24.html
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CVE-2020-13950: mod_proxy_http NULL pointer dereference
Severity: low
Vendor: The Apache Software Foundation
Versions Affected:
httpd 2.4.41 to 2.4.46
Description:
Apache HTTP Server 2.4.41 to 2.4.46
mod_proxy_http can be made to crash (NULL pointer dereference) with specially crafted requests using
both Content-Length and Transfer-Encoding headers, leading to a Denial of Service
Mitigation:
None
Credit:
Reported by Marc Stern (<marc.stern approach.be>)
References:
https://httpd.apache.org/security/vulnerabilities_24.html
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CVE-2020-13938: Improper Handling of Insufficient Privileges
Severity: moderate
Vendor: The Apache Software Foundation
Versions Affected:
httpd 2.4.0 to 2.4.47
Description:
Apache HTTP Server 2.4.0 to 2.4.47
Unprivileged local users can stop httpd on Windows
Mitigation:
n/a
Credit:
Discovered by Ivan Zhakov
References:
https://httpd.apache.org/security/vulnerabilities_24.html
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CVE-2019-17567: mod_proxy_wstunnel tunneling of non Upgraded connections
Severity: moderate
Vendor: The Apache Software Foundation
Versions Affected:
httpd 2.4.6 to 2.4.46
Description:
Apache HTTP Server 2.4.6 to 2.4.46
mod_proxy_wstunnel configured on an URL that is not necessarily Upgraded by the origin server was
tunneling the whole connection regardless, thus allowing for subsequent requests on the same connection
to pass through with no HTTP validation, authentication or authorization possibly configured.
Mitigation:
Configure mod_proxy_wstunnel on URLs that are always Upgraded by the origin server
Credit:
Reported by Mikhail Egorov (<0ang3el gmail.com>)
References:
https://httpd.apache.org/security/vulnerabilities_24.html
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