CVE-2026-86138

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.

This library allows to manipulate XML files. It includes support to read, modify and write XML and HTML files. There is DTDs support this includes parsing and validation even with complex DtDs, either at parse time or later once the document has been modified. The output can be a simple SAX stream or and in-memory DOM like representations. In this case one can use the built-in XPath and XPointer implementation to select sub nodes or ranges. A flexible Input/Output mechanism is available, with existing HTTP and FTP modules and combined to an URI library.

Security Fix(es):

Integer overflow in libxml in Google Chrome prior to 151.0.7922.72 allowed a remote attacker to execute arbitrary code inside a sandbox via a crafted HTML page. (Chromium security severity: High)(CVE-2026-17705)

In libxml2 before 2.15.4, xmlFAParsePosCharGroup has an out-of-bounds read, aka an out-of-bounds read in the NXT macro in xmlregexp.(CVE-2026-86137)

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.(CVE-2026-86138)

In libxml2 before 2.15.4, xmlSnprintfElements in valid.c has a strcat stack-based buffer overflow.(CVE-2026-86140)

This library allows to manipulate XML files. It includes support to read, modify and write XML and HTML files. There is DTDs support this includes parsing and validation even with complex DtDs, either at parse time or later once the document has been modified. The output can be a simple SAX stream or and in-memory DOM like representations. In this case one can use the built-in XPath and XPointer implementation to select sub nodes or ranges. A flexible Input/Output mechanism is available, with existing HTTP and FTP modules and combined to an URI library.

Security Fix(es):

Integer overflow in libxml in Google Chrome prior to 151.0.7922.72 allowed a remote attacker to execute arbitrary code inside a sandbox via a crafted HTML page. (Chromium security severity: High)(CVE-2026-17705)

In libxml2 before 2.15.4, xmlFAParsePosCharGroup has an out-of-bounds read, aka an out-of-bounds read in the NXT macro in xmlregexp.(CVE-2026-86137)

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.(CVE-2026-86138)

In libxml2 before 2.15.4, xmlSnprintfElements in valid.c has a strcat stack-based buffer overflow.(CVE-2026-86140)

This library allows to manipulate XML files. It includes support to read, modify and write XML and HTML files. There is DTDs support this includes parsing and validation even with complex DtDs, either at parse time or later once the document has been modified. The output can be a simple SAX stream or and in-memory DOM like representations. In this case one can use the built-in XPath and XPointer implementation to select sub nodes or ranges. A flexible Input/Output mechanism is available, with existing HTTP and FTP modules and combined to an URI library.

Security Fix(es):

Integer overflow in libxml in Google Chrome prior to 151.0.7922.72 allowed a remote attacker to execute arbitrary code inside a sandbox via a crafted HTML page. (Chromium security severity: High)(CVE-2026-17705)

In libxml2 before 2.15.4, xmlFAParsePosCharGroup has an out-of-bounds read, aka an out-of-bounds read in the NXT macro in xmlregexp.(CVE-2026-86137)

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.(CVE-2026-86138)

In libxml2 before 2.15.4, xmlSnprintfElements in valid.c has a strcat stack-based buffer overflow.(CVE-2026-86140)

This library allows to manipulate XML files. It includes support to read, modify and write XML and HTML files. There is DTDs support this includes parsing and validation even with complex DtDs, either at parse time or later once the document has been modified. The output can be a simple SAX stream or and in-memory DOM like representations. In this case one can use the built-in XPath and XPointer implementation to select sub nodes or ranges. A flexible Input/Output mechanism is available, with existing HTTP and FTP modules and combined to an URI library.

Security Fix(es):

Integer overflow in libxml in Google Chrome prior to 151.0.7922.72 allowed a remote attacker to execute arbitrary code inside a sandbox via a crafted HTML page. (Chromium security severity: High)(CVE-2026-17705)

In libxml2 before 2.15.4, xmlFAParsePosCharGroup has an out-of-bounds read, aka an out-of-bounds read in the NXT macro in xmlregexp.(CVE-2026-86137)

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.(CVE-2026-86138)

In libxml2 before 2.15.4, xmlSnprintfElements in valid.c has a strcat stack-based buffer overflow.(CVE-2026-86140)

This library allows to manipulate XML files. It includes support to read, modify and write XML and HTML files. There is DTDs support this includes parsing and validation even with complex DtDs, either at parse time or later once the document has been modified. The output can be a simple SAX stream or and in-memory DOM like representations. In this case one can use the built-in XPath and XPointer implementation to select sub nodes or ranges. A flexible Input/Output mechanism is available, with existing HTTP and FTP modules and combined to an URI library.

Security Fix(es):

Integer overflow in libxml in Google Chrome prior to 151.0.7922.72 allowed a remote attacker to execute arbitrary code inside a sandbox via a crafted HTML page. (Chromium security severity: High)(CVE-2026-17705)

In libxml2 before 2.15.4, xmlFAParsePosCharGroup has an out-of-bounds read, aka an out-of-bounds read in the NXT macro in xmlregexp.(CVE-2026-86137)

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.(CVE-2026-86138)

In libxml2 before 2.15.4, xmlSnprintfElements in valid.c has a strcat stack-based buffer overflow.(CVE-2026-86140)

The libxml2 library is a development toolbox providing the implementation of various XML standards.

Security Fix(es):

• libxml2: libxml2: Arbitrary code execution via heap-based buffer overflow (CVE-2026-86138)

• libxml2: libxml2: Data integrity issues due to integer overflow in write callbacks (CVE-2026-86143)

• libxml2: libxml2: Arbitrary code execution via stack-based buffer overflow in xmlSnprintfElements (CVE-2026-86140)

• libxml2: libxml2: Heap-based buffer overflow in xmlXPtrEval due to xpointer length saturation (CVE-2026-86142)

• libxml2: libxml2: Information disclosure, SSRF, or denial of service due to improper parseFlags propagation. (CVE-2026-86144)

• libxml2: double-free/UAF in libxml2 Python bindings (CVE-2026-74860)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

The libxml2 library is a development toolbox providing the implementation of various XML standards.

Security Fix(es):

• libxml2: libxml2: Arbitrary code execution via heap-based buffer overflow (CVE-2026-86138)

• libxml2: libxml2: Data integrity issues due to integer overflow in write callbacks (CVE-2026-86143)

• libxml2: libxml2: Arbitrary code execution via stack-based buffer overflow in xmlSnprintfElements (CVE-2026-86140)

• libxml2: libxml2: Heap-based buffer overflow in xmlXPtrEval due to xpointer length saturation (CVE-2026-86142)

• libxml2: libxml2: Information disclosure, SSRF, or denial of service due to improper parseFlags propagation. (CVE-2026-86144)

• libxml2: double-free/UAF in libxml2 Python bindings (CVE-2026-74860)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

The libxml2 library is a development toolbox providing the implementation of various XML standards.

Security Fix(es):

• libxml2: libxml2: Arbitrary code execution via heap-based buffer overflow (CVE-2026-86138)

• libxml2: libxml2: Data integrity issues due to integer overflow in write callbacks (CVE-2026-86143)

• libxml2: libxml2: Arbitrary code execution via stack-based buffer overflow in xmlSnprintfElements (CVE-2026-86140)

• libxml2: libxml2: Information disclosure, SSRF, or denial of service due to improper parseFlags propagation. (CVE-2026-86144)

• libxml2: double-free/UAF in libxml2 Python bindings (CVE-2026-74860)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.

The libxml2 library is a development toolbox providing the implementation of various XML standards.

Security Fix(es):

• libxml2: libxml2: Arbitrary code execution via heap-based buffer overflow (CVE-2026-86138)
• libxml2: libxml2: Data integrity issues due to integer overflow in write callbacks (CVE-2026-86143)
• libxml2: libxml2: Arbitrary code execution via stack-based buffer overflow in xmlSnprintfElements (CVE-2026-86140)
• libxml2: libxml2: Heap-based buffer overflow in xmlXPtrEval due to xpointer length saturation (CVE-2026-86142)
• libxml2: libxml2: Information disclosure, SSRF, or denial of service due to improper parseFlags propagation. (CVE-2026-86144)
• libxml2: double-free/UAF in libxml2 Python bindings (CVE-2026-74860)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

The libxml2 library is a development toolbox providing the implementation of various XML standards.

Security Fix(es):

• libxml2: libxml2: Arbitrary code execution via heap-based buffer overflow (CVE-2026-86138)
• libxml2: libxml2: Data integrity issues due to integer overflow in write callbacks (CVE-2026-86143)
• libxml2: libxml2: Arbitrary code execution via stack-based buffer overflow in xmlSnprintfElements (CVE-2026-86140)
• libxml2: libxml2: Heap-based buffer overflow in xmlXPtrEval due to xpointer length saturation (CVE-2026-86142)
• libxml2: libxml2: Information disclosure, SSRF, or denial of service due to improper parseFlags propagation. (CVE-2026-86144)
• libxml2: double-free/UAF in libxml2 Python bindings (CVE-2026-74860)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

The libxml2 library is a development toolbox providing the implementation of various XML standards.

Security Fix(es):

• libxml2: libxml2: Arbitrary code execution via heap-based buffer overflow (CVE-2026-86138)
• libxml2: libxml2: Data integrity issues due to integer overflow in write callbacks (CVE-2026-86143)
• libxml2: libxml2: Arbitrary code execution via stack-based buffer overflow in xmlSnprintfElements (CVE-2026-86140)
• libxml2: libxml2: Information disclosure, SSRF, or denial of service due to improper parseFlags propagation. (CVE-2026-86144)
• libxml2: double-free/UAF in libxml2 Python bindings (CVE-2026-74860)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.

• CVE-2026-86138: add overflow checks to xmlDictAddQString pool size calculation and bound the QName lengths in its caller xmlDictQLookup to prevent heap buffer overflow when interning long QNames
• CVE-2026-86140: add bounds checks around the englobing parenthesis strcat() calls in xmlSnprintfElements to prevent stack buffer overflow
• CVE-2026-86142: reject XPointer parts whose length is not representable as an int in xmlXPtrEvalXPtrPart to prevent heap buffer overflow

• SECURITY UPDATE: integer overflow leading to heap buffer overflow in xmlDictAddQString
  • debian/patches/CVE-2026-86138.patch: add overflow checks for pool size calculations in xmlDictAddQString() and its sibling xmlDictAddString(), and cap the QName length in xmlDictQLookup(), in dict.c
  • CVE-2026-86138

• CVE-2026-86138: fix integer overflow in xmlDictAddQString pool size calculation causing heap buffer overflow

• CVE-2026-86138: fix integer overflow in xmlDictAddQString pool size calculation that could lead to a heap buffer overflow, and cap the QName lengths accepted by xmlDictQLookup so the guard cannot be skipped

• CVE-2026-86138: fix integer overflow in xmlDictAddQString pool size calculation causing heap buffer overflow

• SECURITY UPDATE: integer overflow leading to heap buffer overflow in xmlDictAddQString()
  • debian/patches/CVE-2026-86138.patch: add SIZE_MAX-based overflow guards to the pool size computation in xmlDictAddQString() in dict.c, plus a SIZE_MAX fallback define, so an oversized prefix and name can no longer wrap the allocation size and let the following memcpy() write past the dictionary string pool
  • CVE-2026-86138

• SECURITY UPDATE: integer overflow leading to heap buffer overflow in xmlDictAddQString()
  • debian/patches/CVE-2026-86138.patch: add SIZE_MAX-based overflow guards to the pool size computation in xmlDictAddQString() in dict.c, plus a SIZE_MAX fallback define, so an oversized prefix and name can no longer wrap the allocation size and let the following memcpy() write past the dictionary string pool
  • CVE-2026-86138

• CVE-2026-86138: add integer-overflow guards to the pool size calculations in xmlDictAddString and xmlDictAddQString, and cap the name and prefix lengths in xmlDictQLookup at INT_MAX/2, preventing an undersized allocation and heap buffer overflow

• CVE-2026-86138: add overflow checks to xmlDictAddQString to prevent an integer overflow and heap buffer overflow
• CVE-2026-86140: bound the writes in xmlSnprintfElements to prevent a stack buffer overflow
• CVE-2026-86142: make xmlStrlen saturate above INT_MAX and reject the saturated length in xmlXPtrEvalXPtrPart to prevent a heap buffer overflow
• CVE-2026-86143: reject buffer lengths at or above INT_MAX before calling the output write callback to prevent an integer overflow
• CVE-2026-86144: propagate parseFlags in xmlXIncludeProcess and xmlXIncludeProcessTree so parser flags such as XML_PARSE_NONET are honoured

• CVE-2026-86138: add overflow checks to xmlDictAddQString pool size calculation and reject over-long QNames in xmlDictQLookup to prevent heap buffer overflow when interning long QNames

• CVE-2026-86138: add overflow checks to xmlDictAddQString pool size calculation and reject over-long QNames in xmlDictQLookup to prevent heap buffer overflow when interning long QNames

• CVE-2026-86138: add overflow checks to xmlDictAddQString pool size calculation and reject over-long QNames in xmlDictQLookup to prevent heap buffer overflow when interning long QNames

• SECURITY UPDATE: heap buffer overflow in the XML dictionary QName interning path
  • debian/patches/CVE-2026-86138.patch: Add integer overflow checks to the pool size calculation in xmlDictAddQString() in dict.c, and cap the prefix and name lengths in xmlDictQLookup() so the sum namelen + plen + 1 cannot wrap and undersize the pool allocation
  • CVE-2026-86138

The updated packages fix several security issues: Stack-Based Buffer Overflow in libxml2. (CVE-2026-11979) In libxml2 before 2.15.4, xmlFAParsePosCharGroup has an out-of-bounds read, aka an out-of-bounds read in the NXT macro in xmlregexp. (CVE-2026-86137) In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow. (CVE-2026-86138) In libxml2 before 2.15.4, xmlURIEscapeStr in uri.c has an integer overflow. (CVE-2026-86139) In libxml2 before 2.15.4, xmlSnprintfElements in valid.c has a strcat stack-based buffer overflow. (CVE-2026-86140) xmlregexp in libxml2 before 2.15.4 has a NULL pointer dereference in xmlRegNewParserCtxt after a strdup failure, i.e., it does not calculate a string length after NULL checking. (CVE-2026-86141) In libxml2 before 2.15.4, there is a heap-based buffer overflow in xmlXPtrEvalXPtrPart because of xmlXPtrEval xpointer length saturation. (CVE-2026-86142) In xmlIO in libxml2 before 2.15.4, an inconsistency in xmlOutputWriteCallback and xmlBufUse causes negative lengths to reach write callbacks, aka a lack of a check for integer overflow before calling writecallback. This has security relevance for many types of uses of that length value within a callback. (CVE-2026-86143) In xinclude in libxml2 before 2.15.4, xmlXIncludeProcess and xmlXIncludeProcessTree do not propagate parseFlags. This has security relevance for, for example, the XML_PARSE_NONET flag, if (without it) a custom resource loader accesses the internet and triggers XML external entity injection, SSRF, or a denial of service (e.g., for an attacker-controlled internet resource that is intentionally slow). (CVE-2026-86144)

Root has patched CVE-2026-86138 in the libxml2 package for Root:Debian:12. Multiple fixed versions available.

Yirou Yang discovered that libxml2 incorrectly handled certain XML catalogs. If a user or automated system was tricked into processing a specially crafted XML catalog, an attacker could possibly use this issue to cause libxml2 to crash, resulting in a denial of service. (CVE-2026-76781)

It was discovered that libxml2 incorrectly handled certain large qualified names, leading to a heap-based buffer overflow. An attacker could possibly use this issue to cause libxml2 to crash, resulting in a denial of service, or possibly execute arbitrary code. (CVE-2026-86138)

It was discovered that libxml2 incorrectly handled escaping certain large URI strings. An attacker could possibly use this issue to cause libxml2 to use excessive resources, leading to a denial of service. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-86139)

Xudong Cao and Meng Xu discovered that libxml2 incorrectly handled certain large XPointer expressions, leading to a heap-based buffer overflow. An attacker could possibly use this issue to cause libxml2 to crash, resulting in a denial of service, or possibly execute arbitrary code. (CVE-2026-86142)

Xudong Cao and Meng Xu discovered that libxml2 did not check for integer overflows before passing output lengths to write callbacks. An attacker could possibly use this issue to cause an application using libxml2 to crash, resulting in a denial of service. (CVE-2026-86143)

It was discovered that libxml2 did not apply parser options, such as disabling network access, when processing XInclude directives under certain circumstances. An attacker could possibly use this issue to perform XML external entity injection or server-side request forgery attacks, or cause a denial of service. (CVE-2026-86144)