The Apache HTTP Server Project patched a path traversal vulnerability introduced less than a month ago that has been exploited in the wild.Update October 7: The Solution section has been updated to reflect the secondary fix the Apache HTTP Server Project released.

CVE-2021-41773: Path Traversal Zero-Day in Apache HTTP Server Exploited

A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. An attacker could use a path traversal attack to map URLs to files outside the directories configured by Alias-like directives. If files outside of these directories are not protected by the usual default configuration "require all denied", these requests can succeed. If CGI scripts are also enabled for these aliased pathes, this could allow for remote code execution. This issue is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions. The fix in Apache HTTP Server 2.4.50 was found to be incomplete, see CVE-2021-42013.

An update of the httpd package has been released.

The remote host is affected by the vulnerability described in GLSA-202208-20 (Apache HTTPD: Multiple Vulnerabilities)

  - A crafted method sent through HTTP/2 will bypass validation and be forwarded by mod_proxy, which can lead     to request splitting or cache poisoning. This issue affects Apache HTTP Server 2.4.17 to 2.4.48.
    (CVE-2021-33193)

  - Malformed requests may cause the server to dereference a NULL pointer. This issue affects Apache HTTP     Server 2.4.48 and earlier. (CVE-2021-34798)

  - A carefully crafted request uri-path can cause mod_proxy_uwsgi to read above the allocated memory and     crash (DoS). This issue affects Apache HTTP Server versions 2.4.30 to 2.4.48 (inclusive). (CVE-2021-36160)

  - ap_escape_quotes() may write beyond the end of a buffer when given malicious input. No included modules     pass untrusted data to these functions, but third-party / external modules may. This issue affects Apache     HTTP Server 2.4.48 and earlier. (CVE-2021-39275)

  - A crafted request uri-path can cause mod_proxy to forward the request to an origin server choosen by the     remote user. This issue affects Apache HTTP Server 2.4.48 and earlier. (CVE-2021-40438)

  - While fuzzing the 2.4.49 httpd, a new null pointer dereference was detected during HTTP/2 request     processing, allowing an external source to DoS the server. This requires a specially crafted request. The     vulnerability was recently introduced in version 2.4.49. No exploit is known to the project.
    (CVE-2021-41524)

  - A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. An attacker could     use a path traversal attack to map URLs to files outside the directories configured by Alias-like     directives. If files outside of these directories are not protected by the usual default configuration     require all denied, these requests can succeed. If CGI scripts are also enabled for these aliased     pathes, this could allow for remote code execution. This issue is known to be exploited in the wild. This     issue only affects Apache 2.4.49 and not earlier versions. The fix in Apache HTTP Server 2.4.50 was found     to be incomplete, see CVE-2021-42013. (CVE-2021-41773)

  - It was found that the fix for CVE-2021-41773 in Apache HTTP Server 2.4.50 was insufficient. An attacker     could use a path traversal attack to map URLs to files outside the directories configured by Alias-like     directives. If files outside of these directories are not protected by the usual default configuration     require all denied, these requests can succeed. If CGI scripts are also enabled for these aliased     pathes, this could allow for remote code execution. This issue only affects Apache 2.4.49 and Apache     2.4.50 and not earlier versions. (CVE-2021-42013)

  - A crafted URI sent to httpd configured as a forward proxy (ProxyRequests on) can cause a crash (NULL     pointer dereference) or, for configurations mixing forward and reverse proxy declarations, can allow for     requests to be directed to a declared Unix Domain Socket endpoint (Server Side Request Forgery). This     issue affects Apache HTTP Server 2.4.7 up to 2.4.51 (included). (CVE-2021-44224)

  - A carefully crafted request body can cause a buffer overflow in the mod_lua multipart parser     (r:parsebody() called from Lua scripts). The Apache httpd team is not aware of an exploit for the     vulnerability though it might be possible to craft one. This issue affects Apache HTTP Server 2.4.51 and     earlier. (CVE-2021-44790)

  - A carefully crafted request body can cause a read to a random memory area which could cause the process to     crash. This issue affects Apache HTTP Server 2.4.52 and earlier. (CVE-2022-22719)

  - Apache HTTP Server 2.4.52 and earlier fails to close inbound connection when errors are encountered     discarding the request body, exposing the server to HTTP Request Smuggling (CVE-2022-22720)

  - If LimitXMLRequestBody is set to allow request bodies larger than 350MB (defaults to 1M) on 32 bit systems     an integer overflow happens which later causes out of bounds writes. This issue affects Apache HTTP Server     2.4.52 and earlier. (CVE-2022-22721)

  - Out-of-bounds Write vulnerability in mod_sed of Apache HTTP Server allows an attacker to overwrite heap     memory with possibly attacker provided data. This issue affects Apache HTTP Server 2.4 version 2.4.52 and     prior versions. (CVE-2022-23943)

  - Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling') vulnerability in mod_proxy_ajp of     Apache HTTP Server allows an attacker to smuggle requests to the AJP server it forwards requests to. This     issue affects Apache HTTP Server Apache HTTP Server 2.4 version 2.4.53 and prior versions.
    (CVE-2022-26377)

  - The ap_rwrite() function in Apache HTTP Server 2.4.53 and earlier may read unintended memory if an     attacker can cause the server to reflect very large input using ap_rwrite() or ap_rputs(), such as with     mod_luas r:puts() function. Modules compiled and distributed separately from Apache HTTP Server that use     the 'ap_rputs' function and may pass it a very large (INT_MAX or larger) string must be compiled against     current headers to resolve the issue. (CVE-2022-28614)

  - Apache HTTP Server 2.4.53 and earlier may crash or disclose information due to a read beyond bounds in     ap_strcmp_match() when provided with an extremely large input buffer. While no code distributed with the     server can be coerced into such a call, third-party modules or lua scripts that use ap_strcmp_match() may     hypothetically be affected. (CVE-2022-28615)

  - In Apache HTTP Server 2.4.53 and earlier, a malicious request to a lua script that calls r:parsebody(0)     may cause a denial of service due to no default limit on possible input size. (CVE-2022-29404)

  - If Apache HTTP Server 2.4.53 is configured to do transformations with mod_sed in contexts where the input     to mod_sed may be very large, mod_sed may make excessively large memory allocations and trigger an abort.
    (CVE-2022-30522)

  - Apache HTTP Server 2.4.53 and earlier may return lengths to applications calling r:wsread() that point     past the end of the storage allocated for the buffer. (CVE-2022-30556)

  - Apache HTTP Server 2.4.53 and earlier may not send the X-Forwarded-* headers to the origin server based on     client side Connection header hop-by-hop mechanism. This may be used to bypass IP based authentication on     the origin server/application. (CVE-2022-31813)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of httpd24 installed on the remote host is prior to 2.4.51-1.94. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS-2021-1543 advisory.

    A NULL pointer dereference was found in Apache httpd mod_h2. The highest threat from this flaw is to     system integrity. (CVE-2021-33193)

    A NULL pointer dereference in httpd allows an unauthenticated remote attacker to crash httpd by providing     malformed HTTP requests. The highest threat from this vulnerability is to system availability.
    (CVE-2021-34798)

    An out-of-bounds read in mod_proxy_uwsgi of httpd allows a remote unauthenticated attacker to crash the     service through a crafted request. The highest threat from this vulnerability is to system availability.
    (CVE-2021-36160)

    An out-of-bounds write in function ap_escape_quotes of httpd allows an unauthenticated remote attacker to     crash the server or potentially execute code on the system with the privileges of the httpd user, by     providing malicious input to the function. (CVE-2021-39275)

    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. (CVE-2021-40438)

    While fuzzing the 2.4.49 httpd, a new null pointer dereference was detected during HTTP/2 request     processing, allowing an external source to DoS the server. This requires a specially crafted request. The     vulnerability was recently introduced in version 2.4.49. No exploit is known to the project.
    (CVE-2021-41524)

    A path transversal flaw was found in Apache 2.4.49. A remote attacker could use this flaw to map URLs to     files outside the expected document root. Additionally this flaw could leak the source of interpreted     files like CGI scripts. (CVE-2021-41773)

    A path transversal and remote code execution flaw was found in Apache HTTP Server 2.4.49 and 2.4.50. A     remote attacker could use this flaw to map URLs to files outside the expected document root. Additionally,     this flaw could leak the source of interpreted files like CGI scripts. If files outside of these     directories are not protected by the usual default configuration require all denied, these requests can     succeed. If CGI scripts are also enabled for these aliased paths, this could allow for remote code     execution. The highest threat from this vulnerability is to data confidentiality and integrity as well as     system availability. This is an incomplete fix for CVE-2021-41773. (CVE-2021-42013)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of httpd installed on the remote host is prior to 2.4.51-1. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2021-1716 advisory.

    A NULL pointer dereference was found in Apache httpd mod_h2. The highest threat from this flaw is to     system integrity. (CVE-2021-33193)

    A NULL pointer dereference in httpd allows an unauthenticated remote attacker to crash httpd by providing     malformed HTTP requests. The highest threat from this vulnerability is to system availability.
    (CVE-2021-34798)

    An out-of-bounds read in mod_proxy_uwsgi of httpd allows a remote unauthenticated attacker to crash the     service through a crafted request. The highest threat from this vulnerability is to system availability.
    (CVE-2021-36160)

    An out-of-bounds write in function ap_escape_quotes of httpd allows an unauthenticated remote attacker to     crash the server or potentially execute code on the system with the privileges of the httpd user, by     providing malicious input to the function. (CVE-2021-39275)

    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. (CVE-2021-40438)

    While fuzzing the 2.4.49 httpd, a new null pointer dereference was detected during HTTP/2 request     processing, allowing an external source to DoS the server. This requires a specially crafted request. The     vulnerability was recently introduced in version 2.4.49. No exploit is known to the project.
    (CVE-2021-41524)

    A path transversal flaw was found in Apache 2.4.49. A remote attacker could use this flaw to map URLs to     files outside the expected document root. Additionally this flaw could leak the source of interpreted     files like CGI scripts. (CVE-2021-41773)

    A path transversal and remote code execution flaw was found in Apache HTTP Server 2.4.49 and 2.4.50. A     remote attacker could use this flaw to map URLs to files outside the expected document root. Additionally,     this flaw could leak the source of interpreted files like CGI scripts. If files outside of these     directories are not protected by the usual default configuration require all denied, these requests can     succeed. If CGI scripts are also enabled for these aliased paths, this could allow for remote code     execution. The highest threat from this vulnerability is to data confidentiality and integrity as well as     system availability. This is an incomplete fix for CVE-2021-41773. (CVE-2021-42013)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Apache http server project reports :

- moderate: NULL pointer dereference in h2 fuzzing (CVE-2021-41524)

- important: Path traversal and file disclosure vulnerability in Apache HTTP Server 2.4.49 (CVE-2021-41773)

According to its banner, the version of Apache running on the remote host is 2.4.49. It is, therefore, affected by multiple vulnerabilities:

 - While fuzzing the 2.4.49 httpd, a new null pointer dereference was detected during HTTP/2 request processing, allowing an external source to DoS the server. This requires a specially crafted request. The vulnerability was recently introduced in version 2.4.49. No exploit is known to the project. (CVE-2021-41524)

 - A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. An attacker could use a path traversal attack to map URLs to files outside the expected document root. If files outside of the document root are not protected by require all denied these requests can succeed. Additionally this flaw could leak the source of interpreted files like CGI scripts. This issue is known to be exploited in the wild. This issue only affects Apache 2.4.49 and not earlier versions. (CVE-2021-41773) Note that the scanner has not tested for these issues but has instead relied only on the application's self-reported version number.

The instance of Apache HTTP Server running on the remote host is affected by a path traversal vulnerability. A remote, unauthenticated attacker can exploit this issue, via a specially crafted HTTP request, to access arbitrary files on the remote host.

The version of Apache httpd installed on the remote host is 2.4.49. It is, therefore, affected by multiple vulnerabilities as referenced in the 2.4.50 advisory.

  - While fuzzing the 2.4.49 httpd, a new null pointer dereference was detected during HTTP/2 request     processing, allowing an external source to DoS the server. This requires a specially crafted request. The     vulnerability was recently introduced in version 2.4.49. No exploit is known to the project.
    (CVE-2021-41524)

  - A flaw was found in a change made to path normalization in Apache HTTP Server 2.4.49. An attacker could     use a path traversal attack to map URLs to files outside the expected document root. If files outside of     the document root are not protected by require all denied these requests can succeed. Additionally this     flaw could leak the source of interpreted files like CGI scripts. This issue is known to be exploited in     the wild. This issue only affects Apache 2.4.49 and not earlier versions. (CVE-2021-41773)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

ID	Name	Product	Family	Severity
203476	Photon OS 4.0: Httpd PHSA-2021-4.0-0118	Nessus	PhotonOS Local Security Checks	critical
164114	GLSA-202208-20 : Apache HTTPD: Multiple Vulnerabilities	Nessus	Gentoo Local Security Checks	critical
154188	Amazon Linux AMI : httpd24 (ALAS-2021-1543)	Nessus	Amazon Linux Local Security Checks	critical
154179	Amazon Linux 2 : httpd (ALAS-2021-1716)	Nessus	Amazon Linux Local Security Checks	critical
153894	FreeBSD : Apache httpd -- Multiple vulnerabilities (25b78bdd-25b8-11ec-a341-d4c9ef517024)	Nessus	FreeBSD Local Security Checks	high
113014	Apache 2.4.49 < 2.4.50 Multiple Vulnerabilities	Web App Scanning	Component Vulnerability	high
153885	Apache HTTP Server 2.4.49 Path Traversal (CVE-2021-41773)	Nessus	CGI abuses	high
153884	Apache 2.4.49 < 2.4.50 Multiple Vulnerabilities	Nessus	Web Servers	high

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