Security Bulletin: IBM HTTP Server is affected by multiple vulnerabilities due to the included Apache HTTP Server and libexpat

Vulnerability Details

CVEID:   CVE-2026-66046
DESCRIPTION:   Expat through 2.8.3 contains a denial of service vulnerability caused by quadratic algorithmic complexity in the storeAtts() function in xmlparse.c, where processing N specified attributes with non-normalized values triggers an O(N^2) linear scan of elementType-defaultAtts to determine CDATA status. A remote unauthenticated attacker can supply a single well-formed XML document of a few megabytes to an application parsing untrusted XML to cause excessive CPU consumption, resulting in denial of service without requiring authentication, external entity resolution, or non-default parser options.
CWE:   CWE-407: Inefficient Algorithmic Complexity
CVSS Source:   disclosure@vulncheck.com
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

CVEID:   CVE-2026-76641
DESCRIPTION:   Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers to trigger memory corruption by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. A struct size mismatch between ELEMENT_TYPE members causes storeAtts to read the attIndex member past allocated memory boundaries, resulting in failure to normalize whitespace in non-CDATA attributes or a wild pointer dereference causing a segfault. This vulnerability was introduced by the fix for CVE-2026-66046.
CWE:   CWE-125: Out-of-bounds Read
CVSS Source:   disclosure@vulncheck.com
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

CVEID:   CVE-2026-42356
DESCRIPTION:   Deployment of wrong handler vulnerability in Apache HTTP Server allows the target of some internal redirects from CGI programs to also be treated as CGI and executed. The target must already be in a directory enabled for CGI and have no other extension understood by mod_mime. This issue affects Apache HTTP Server: from 2.4.60 through 2.4.68.
CWE:   CWE-430: Deployment of Wrong Handler
CVSS Source:   CISA ADP
CVSS Base score:   3.7
CVSS Vector:   (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N)

CVEID:   CVE-2026-42528
DESCRIPTION:   A memory calculation bug in mod_dav in Apache httpd 2.4.67 and earlier allows an attacker with permission to create WebDAV locks to crash server child processes. Users are recommended to upgrade to version 2.4.69, which fixes this issue
CWE:   CWE-789: Memory Allocation with Excessive Size Value
CVSS Source:   CISA ADP
CVSS Base score:   4.3
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L)

CVEID:   CVE-2026-56153
DESCRIPTION:   Out-of-bounds Write vulnerability in Apache HTTP Server's mod_charset_lite. This issue affects Apache HTTP Server: from 2.4.0 through 2.4.68.
CWE:   CWE-787: Out-of-bounds Write
CVSS Source:   CISA ADP
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N)

CVEID:   CVE-2026-56154
DESCRIPTION:   Use After Free vulnerability in Apache HTTP Server's mod_rewrite when using lookahead (%{LA-U:HTTP:...}) This issue affects Apache HTTP Server: from 2.4.0 through 2.4.68.
CWE:   CWE-416: Use After Free
CVSS Source:   CISA ADP
CVSS Base score:   9.8
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)

CVEID:   CVE-2026-59685
DESCRIPTION:   Out-of-bounds Write vulnerability in Apache HTTP Server on Windows while processing paths with 8.3 names that may grow when expanded. This issue affects Apache HTTP Server: from 2.4.0 through 2.4.68.
CWE:   CWE-787: Out-of-bounds Write
CVSS Source:   CISA ADP
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N)

CVEID:   CVE-2026-63045
DESCRIPTION:   Improper validation of FTP PASV reply address in mod_proxy_ftp in Apache Software Foundation Apache HTTP Server through 2.4.68 on all platforms allows, in forward proxy configurations, an untrusted FTP server to cause the proxy to open a data connection to an arbitrary third-party host via a crafted PASV response. Users are recommended to upgrade to version 2.4.69, which fixes this issue.
CWE:   CWE-284: Improper Access Control
CVSS Source:   CISA ADP
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N)

CVEID:   CVE-2026-58415
DESCRIPTION:   Internal state files accessible to external parties in mod_dav_fs in Apache Software Foundation Apache HTTP Server before 2.4.69 on all platforms allows a remote client to read WebDAV dead properties of resources it cannot author via a GET request for the .DAV state directory This issue affects Apache HTTP Server: from 2.4.0 through 2.4.68.
CWE:   CWE-552: Files or Directories Accessible to External Parties
CVSS Source:   CISA ADP
CVSS Base score:   5.3
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)

CVEID:   CVE-2026-79768
DESCRIPTION:   Path equivalence: '/./' (single dot directory) vulnerability in Apache HTTP Server's mod_userdir module when configured with absolute non-wildcard UserDir directive (the 2nd form in https://httpd.apache.org/docs/2.4/mod/mod_userdir.html#userdir) This issue affects Apache HTTP Server: from 2.4.0 through 2.4.68.
CWE:   CWE-55: Path Equivalence: '/./' (Single Dot Directory)
CVSS Source:   CISA ADP
CVSS Base score:   5.3
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)

CVEID:   CVE-2026-93546
DESCRIPTION:   Integer overflow in mod_dav_fs in Apache HTTP Server through 2.4.68 allows an authenticated WebDAV client with write access to crash worker processes and persistently corrupt a directory's property database via PROPPATCH requests declaring many XML namespaces.
CWE:   CWE-190: Integer Overflow or Wraparound
CVSS Source:   CISA ADP
CVSS Base score:   8.8
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)

CVEID:   CVE-2026-63292
DESCRIPTION:   Stack-based buffer overflow in mod_vhost_alias in Apache Software Foundation Apache HTTP Server through 2.4.68 on all platforms allows a remote client to cause a denial of service or potentially execute arbitrary code via an HTTP request with a Host header exceeding 8192 bytes when VirtualDocumentRoot uses a hostname format specifier and LimitRequestFieldSize is raised above the default. Users are recommended to upgrade to version 2.4.69, which fixes this issue.
CWE:   CWE-121: Stack-based Buffer Overflow
CVSS Source:   CISA ADP
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

CVEID:   CVE-2026-76956
DESCRIPTION:   In libexpat 2.8.2 and 2.8.3 before 2.8.4, misinterpretation of getentropy's return code leads to insufficient entropy, which results in being vulnerable to hash flooding attacks, causing a denial of service via crafted XML content.
CWE:   CWE-394: Unexpected Status Code or Return Value
CVSS Source:   NVD
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

CVEID:   CVE-2026-93990
DESCRIPTION:   Expat before 2.8.5 fails to validate that a high surrogate in UTF-16 input is followed by a low surrogate, allowing malformed UTF-16 sequences to be accepted. Attackers can supply UTF-16 encoded XML containing lone high surrogates that consume the following code unit, causing Expat to pass unpaired surrogates to applications built with XML_UNICODE and to silently replace input characters in other builds.
CWE:   CWE-176: Improper Handling of Unicode Encoding
CVSS Source:   disclosure@vulncheck.com
CVSS Base score:   7.5
CVSS Vector:   (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)