CVE-2025-24294

A denial of service vulnerability has been discovered in the resolv gem bundled with Ruby.

Details

The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet.

An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name.

This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.

Affected Version

The vulnerability affects the resolv gem bundled with the following Ruby series:

• Ruby 3.2 series: resolv version 0.2.2 and earlier
• Ruby 3.3 series: resolv version 0.3.0
• Ruby 3.4 series: resolv version 0.6.1 and earlier

Credits

Thanks to Manu for discovering this issue.

History

Originally published at 2025-07-08 07:00:00 (UTC)

Ruby is a fast and easy interpreted scripting language for object-oriented programming. It has many functions for processing text Files and perform system management tasks (such as Perl).

Security Fix(es):

The attack vector is a potential Denial of Service (DoS). The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet.

An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name.

This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.(CVE-2025-24294)

zlib is a Ruby interface for the zlib compression/decompression library. Versions 3.0.0 and below, 3.1.0, 3.1.1, 3.2.0 and 3.2.1 contain a buffer overflow vulnerability in the Zlib::GzipReader. The zstream_buffer_ungets function prepends caller-provided bytes ahead of previously produced output but fails to guarantee the backing Ruby string has enough capacity before the memmove shifts the existing data. This can lead to memory corruption when the buffer length exceeds capacity. This issue has been fixed in versions 3.0.1, 3.1.2 and 3.2.3.(CVE-2026-27820)

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to 0.6.5 and 0.5.15, several Net::IMAP commands accept a "raw data" argument that is sent verbatim after validation to prevent command injection. However, if a server does not support non-synchronizing literals, it may still be possible to inject arbitrary IMAP commands inside non-synchronizing literals. A server without support for non-synchronizing literals may interpret the "+}\r\n" as the end of a malformed command line and respond with a tagged BAD. In that case, the contents of the literal will be interpreted as one or more new pipelined commands, allowing a CRLF command injection attack to succeed. This affects criteria for #search and #uid_search; search_keys for #sort, #thread, #uid_sort, and #uid_thread; and attr for #fetch and #uid_fetch. This vulnerability is fixed in 0.6.5 and 0.5.15.(CVE-2026-47240)

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to 0.6.5 and 0.5.15, several Net::IMAP commands accept a raw string argument which is only validated to prevent CRLF injection and then sent verbatim. If this string is derived from user-controlled input, an attacker can force the next command to be absorbed as a continuation of the first command. This will cause the first command to eventually fail, but also prevents it from returning until another command is sent (from another thread). That other command will not return until the connection is closed. This vulnerability is fixed in 0.6.5 and 0.5.15.(CVE-2026-47241)

Ruby is a fast and easy interpreted scripting language for object-oriented programming. It has many functions for processing text Files and perform system management tasks (such as Perl).

Security Fix(es):

The attack vector is a potential Denial of Service (DoS). The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet.

An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name.

This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.(CVE-2025-24294)

zlib is a Ruby interface for the zlib compression/decompression library. Versions 3.0.0 and below, 3.1.0, 3.1.1, 3.2.0 and 3.2.1 contain a buffer overflow vulnerability in the Zlib::GzipReader. The zstream_buffer_ungets function prepends caller-provided bytes ahead of previously produced output but fails to guarantee the backing Ruby string has enough capacity before the memmove shifts the existing data. This can lead to memory corruption when the buffer length exceeds capacity. This issue has been fixed in versions 3.0.1, 3.1.2 and 3.2.3.(CVE-2026-27820)

Ruby is a fast and easy interpreted scripting language for object-oriented programming. It has many functions for processing text Files and perform system management tasks (such as Perl).

Security Fix(es):

The attack vector is a potential Denial of Service (DoS). The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet.

An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name.

This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.(CVE-2025-24294)

zlib is a Ruby interface for the zlib compression/decompression library. Versions 3.0.0 and below, 3.1.0, 3.1.1, 3.2.0 and 3.2.1 contain a buffer overflow vulnerability in the Zlib::GzipReader. The zstream_buffer_ungets function prepends caller-provided bytes ahead of previously produced output but fails to guarantee the backing Ruby string has enough capacity before the memmove shifts the existing data. This can lead to memory corruption when the buffer length exceeds capacity. This issue has been fixed in versions 3.0.1, 3.1.2 and 3.2.3.(CVE-2026-27820)

Ruby is a fast and easy interpreted scripting language for object-oriented programming. It has many functions for processing text Files and perform system management tasks (such as Perl).

Security Fix(es):

The attack vector is a potential Denial of Service (DoS). The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet.

An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name.

This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.(CVE-2025-24294)

zlib is a Ruby interface for the zlib compression/decompression library. Versions 3.0.0 and below, 3.1.0, 3.1.1, 3.2.0 and 3.2.1 contain a buffer overflow vulnerability in the Zlib::GzipReader. The zstream_buffer_ungets function prepends caller-provided bytes ahead of previously produced output but fails to guarantee the backing Ruby string has enough capacity before the memmove shifts the existing data. This can lead to memory corruption when the buffer length exceeds capacity. This issue has been fixed in versions 3.0.1, 3.1.2 and 3.2.3.(CVE-2026-27820)

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to 0.6.5 and 0.5.15, several Net::IMAP commands accept a "raw data" argument that is sent verbatim after validation to prevent command injection. However, if a server does not support non-synchronizing literals, it may still be possible to inject arbitrary IMAP commands inside non-synchronizing literals. A server without support for non-synchronizing literals may interpret the "+}\r\n" as the end of a malformed command line and respond with a tagged BAD. In that case, the contents of the literal will be interpreted as one or more new pipelined commands, allowing a CRLF command injection attack to succeed. This affects criteria for #search and #uid_search; search_keys for #sort, #thread, #uid_sort, and #uid_thread; and attr for #fetch and #uid_fetch. This vulnerability is fixed in 0.6.5 and 0.5.15.(CVE-2026-47240)

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to 0.6.5 and 0.5.15, several Net::IMAP commands accept a raw string argument which is only validated to prevent CRLF injection and then sent verbatim. If this string is derived from user-controlled input, an attacker can force the next command to be absorbed as a continuation of the first command. This will cause the first command to eventually fail, but also prevents it from returning until another command is sent (from another thread). That other command will not return until the connection is closed. This vulnerability is fixed in 0.6.5 and 0.5.15.(CVE-2026-47241)

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to 0.6.5 and 0.5.15, when Net::IMAP#id is called with a hash argument, although the ID field value strings are correctly quoted (escaping quoted specials), they were not validated to prohibit CRLF sequences. While Net::IMAP#enable does process its arguments for aliases, it does not validate them as valid atoms (or as a list of valid atoms). The #to_s value is sent verbatim. Arguments to either command could be used by an attacker to inject arbitrary IMAP commands. This vulnerability is fixed in 0.6.5 and 0.5.15.(CVE-2026-47242)

Ruby is a fast and easy interpreted scripting language for object-oriented programming. It has many functions for processing text Files and perform system management tasks (such as Perl).

Security Fix(es):

The attack vector is a potential Denial of Service (DoS). The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet.

An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name.

This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.(CVE-2025-24294)

zlib is a Ruby interface for the zlib compression/decompression library. Versions 3.0.0 and below, 3.1.0, 3.1.1, 3.2.0 and 3.2.1 contain a buffer overflow vulnerability in the Zlib::GzipReader. The zstream_buffer_ungets function prepends caller-provided bytes ahead of previously produced output but fails to guarantee the backing Ruby string has enough capacity before the memmove shifts the existing data. This can lead to memory corruption when the buffer length exceeds capacity. This issue has been fixed in versions 3.0.1, 3.1.2 and 3.2.3.(CVE-2026-27820)

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to 0.6.5 and 0.5.15, several Net::IMAP commands accept a "raw data" argument that is sent verbatim after validation to prevent command injection. However, if a server does not support non-synchronizing literals, it may still be possible to inject arbitrary IMAP commands inside non-synchronizing literals. A server without support for non-synchronizing literals may interpret the "+}\r\n" as the end of a malformed command line and respond with a tagged BAD. In that case, the contents of the literal will be interpreted as one or more new pipelined commands, allowing a CRLF command injection attack to succeed. This affects criteria for #search and #uid_search; search_keys for #sort, #thread, #uid_sort, and #uid_thread; and attr for #fetch and #uid_fetch. This vulnerability is fixed in 0.6.5 and 0.5.15.(CVE-2026-47240)

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to 0.6.5 and 0.5.15, several Net::IMAP commands accept a raw string argument which is only validated to prevent CRLF injection and then sent verbatim. If this string is derived from user-controlled input, an attacker can force the next command to be absorbed as a continuation of the first command. This will cause the first command to eventually fail, but also prevents it from returning until another command is sent (from another thread). That other command will not return until the connection is closed. This vulnerability is fixed in 0.6.5 and 0.5.15.(CVE-2026-47241)

Ruby is an extensible, interpreted, object-oriented, scripting language. It has features to process text files and to perform system management tasks.

Security Fix(es):

• resolv: Denial of Service in resolv gem (CVE-2025-24294)

• rexml: REXML denial of service (CVE-2025-58767)

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.

Ruby is an extensible, interpreted, object-oriented, scripting language. It has features to process text files and to perform system management tasks.

Security Fix(es):

• resolv: Denial of Service in resolv gem (CVE-2025-24294)

• rexml: REXML denial of service (CVE-2025-58767)

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.

Ruby is an extensible, interpreted, object-oriented, scripting language. It has features to process text files and to perform system management tasks.

Security Fix(es):

• resolv: Denial of Service in resolv gem (CVE-2025-24294)

• rexml: REXML denial of service (CVE-2025-58767)

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 attack vector is a potential Denial of Service (DoS). The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet. An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name. This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.

Ruby is an extensible, interpreted, object-oriented, scripting language. It has features to process text files and to perform system management tasks.

Security Fix(es):

• resolv: Denial of Service in resolv gem (CVE-2025-24294)
• rexml: REXML denial of service (CVE-2025-58767)

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.

Ruby is an extensible, interpreted, object-oriented, scripting language. It has features to process text files and to perform system management tasks.

Security Fix(es):

• resolv: Denial of Service in resolv gem (CVE-2025-24294)
• rexml: REXML denial of service (CVE-2025-58767)

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.

Ruby is an extensible, interpreted, object-oriented, scripting language. It has features to process text files and to perform system management tasks.

Security Fix(es):

• resolv: Denial of Service in resolv gem (CVE-2025-24294)
• rexml: REXML denial of service (CVE-2025-58767)

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 attack vector is a potential Denial of Service (DoS). The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet.

An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name.

This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.

The attack vector is a potential Denial of Service (DoS). The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet.

An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name.

This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.

• CVE-2025-24294: fix decompressed name length limit in DNS resolver to prevent exceeding RFC 1035's 255-octet maximum

• CVE-2025-24294: Limit the length of a decompressed domain name to prevent DoS in resolv gem

The attack vector is a potential Denial of Service (DoS). The vulnerability is caused by an insufficient check on the length of a decompressed domain name within a DNS packet.

An attacker can craft a malicious DNS packet containing a highly compressed domain name. When the resolv library parses such a packet, the name decompression process consumes a large amount of CPU resources, as the library does not limit the resulting length of the name.

This resource consumption can cause the application thread to become unresponsive, resulting in a Denial of Service condition.

This update for ruby2.5 fixes the following issues:

• CVE-2025-24294: resolv: insufficient checks on the length of a decompressed domain name when processing a DNS packet can lead to a denial of service due to excessive resource consumption (bsc#1246430).

This update for ruby2.5 fixes the following issues:

• CVE-2024-35221: Fixed remote DoS via YAML manifest (bsc#1225905)
• CVE-2024-47220: Fixed HTTP request smuggling in WEBrick (bsc#1230930)
• CVE-2024-49761: Fixed ReDOS vulnerability by updating REXML to 3.3.9 (bsc#1232440)
• CVE-2025-24294: Fixed denial of service (DoS) caused by an insufficient check on the length of a decompressed domain name within a DNS packet in resolv gem (bsc#1246430)
• CVE-2025-27219: Fixed denial of service in CGI::Cookie.parse (bsc#1237804)
• CVE-2025-27220: Fixed ReDoS in CGI::Util#escapeElement (bsc#1237806)
• CVE-2025-27221: Fixed userinfo leakage in URI#join, URI#merge and URI#+ (bsc#1237805)
• CVE-2025-6442: Fixed ruby WEBrick read_header HTTP request smuggling vulnerability (bsc#1245254)

It was discovered that Ruby incorrectly handled certain IO stream methods. A remote attacker could use this issue to cause Ruby to crash, resulting in a denial of service, or possibly obtain sensitive information. This issue only affected Ubuntu 18.04 LTS. (CVE-2024-27280)

It was discovered that the Ruby regex compiler incorrectly handled certain memory operations. A remote attacker could possibly use this issue to obtain sensitive memory contents. This issue only affected Ubuntu 18.04 LTS. (CVE-2024-27282)

It was discovered that Ruby incorrectly handled parsing of certain XML characters through the REXML gem. An attacker could use this issue to cause Ruby to crash, resulting in a denial of service. This issue only affected Ubuntu 18.04 LTS. (CVE-2024-35176)

It was discovered that Ruby incorrectly handled decompressed domain names within a DNS packet. An attacker could use this issue to cause Ruby to crash, resulting in a denial of service. (CVE-2025-24294)

It was discovered that RubyGems incorrectly handled certain regular expressions. An attacker could use this issue to cause RubyGems to crash, resulting in a denial of service. This issue only affected Ubuntu 22.04 LTS. (CVE-2023-28755)

It was discovered that RubyGems incorrectly handled decompressed domain names within a DNS packet. An attacker could use this issue to cause RubyGems to crash, resulting in a denial of service. This issue only affected Ubuntu 25.04. (CVE-2025-24294)