{"id":34123,"date":"2025-05-02T05:40:50","date_gmt":"2025-05-02T05:40:50","guid":{"rendered":""},"modified":"2025-09-16T07:09:01","modified_gmt":"2025-09-16T13:09:01","slug":"cve-2025-43859-critical-vulnerability-in-h11-python-http-1-1-implementation","status":"publish","type":"post","link":"https:\/\/www.ameeba.com\/blog\/cve-2025-43859-critical-vulnerability-in-h11-python-http-1-1-implementation\/","title":{"rendered":"<strong>CVE-2025-43859: Critical Vulnerability in h11 Python HTTP\/1.1 Implementation<\/strong>"},"content":{"rendered":"<p><strong>Overview<\/strong><\/p>\n<p>The cybersecurity community has recently identified a serious vulnerability in the h11 Python HTTP\/1.1 implementation. This flaw, recognized as CVE-2025-43859, has the potential to compromise systems and leak sensitive data under certain conditions. It&#8217;s a critical issue that mainly affects developers and organizations that use versions of <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2025-32825-critical-sql-injection-vulnerability-in-telecontrol-server-basic\/\"  data-wpil-monitor-id=\"38779\">h11<\/a> prior to 0.16.0 in conjunction with certain buggy proxy servers. The <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2025-1290-high-severity-race-condition-use-after-free-vulnerability-in-kernel-5-4-on-chromeos\/\"  data-wpil-monitor-id=\"41780\">severity of this vulnerability<\/a> is underscored by its CVSS Severity Score of 9.1, indicating a high level of risk.<\/p>\n<p><strong>Vulnerability Summary<\/strong><\/p>\n<p>CVE ID: CVE-2025-43859<br \/>\nSeverity: Critical &#8211; CVSS 9.1<br \/>\nAttack Vector: Network<br \/>\nPrivileges Required: None<br \/>\nUser Interaction: None<br \/>\nImpact: <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2025-3914-potential-arbitrary-file-uploads-and-system-compromise-in-aeropage-sync-for-airtable-wordpress-plugin\/\"  data-wpil-monitor-id=\"40806\">System compromise<\/a>, potential data leakage<\/p>\n<p><strong>Affected Products<\/strong><\/p><div id=\"ameeb-438272776\" class=\"ameeb-content-2 ameeb-entity-placement\"><div style=\"border-left: 4px solid #555; padding-left: 20px; margin: 48px 0; font-family: Roboto, sans-serif; color: #ffffff; line-height: 1.6; max-width: 700px;\">\r\n  <h2 style=\"margin-top: 0; font-size: 20px; font-weight: 600; display: flex; align-items: center;\">\r\n    <a href=\"https:\/\/www.ameeba.com\/chat\" style=\"display: inline-flex; align-items: center; margin-right: 8px;\">\r\n      <img decoding=\"async\" src=\"https:\/\/www.ameeba.com\/blog\/wp-content\/uploads\/2025\/10\/Best-App-icon-Ameeba.png\" alt=\"Ameeba Chat Icon\" style=\"width: 40px; height: 40px;\" \/>\r\n    <\/a>\r\n    A new way to communicate\r\n  <\/h2>\r\n\r\n  <p style=\"margin-bottom: 12px;\">\r\n    Ameeba Chat is built on encrypted identity, not personal profiles.\r\n  <\/p>\r\n\r\n  <p style=\"margin-bottom: 16px;\">\r\n    Message, call, share files, and coordinate with identities kept separate.\r\n  <\/p>\r\n\r\n  <ul style=\"list-style: none; padding-left: 0; margin-bottom: 20px;\">\r\n    <li>\u2022 Encrypted identity<\/li>\r\n    <li>\u2022 Ameeba Chat authenticates access<\/li>\r\n    <li>\u2022 Aliases and categories<\/li>\r\n    <li>\u2022 End-to-end encrypted chat, calls, and files<\/li>\r\n    <li>\u2022 Secure notes for sensitive information<\/li>\r\n  <\/ul>\r\n\r\n  <p style=\"font-style: italic; font-weight: 600; margin-bottom: 24px;\">\r\n    Private communication, rethought.\r\n  <\/p>\r\n\r\n  <div style=\"display: flex; flex-wrap: wrap; gap: 12px;\">\r\n    <a href=\"https:\/\/www.ameeba.com\/chat\/download\" style=\"background-color: #ffffff; color: #000000; padding: 10px 20px; text-decoration: none; border-radius: 6px; font-weight: 500;\">Download Ameeba Chat<\/a>\r\n    <a href=\"https:\/\/www.ameeba.com\/chat\" style=\"border: 1px solid #ffffff; color: #ffffff; padding: 10px 20px; text-decoration: none; border-radius: 6px; font-weight: 500;\">Learn More<\/a>\r\n  <\/div>\r\n<\/div>\r\n<\/div>\n<p>Product | Affected Versions<\/p>\n<p>h11 Python HTTP\/1.1 implementation | Prior to 0.16.0<\/p>\n<p><strong>How the Exploit Works<\/strong><\/p>\n<p>The <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2021-45465-critical-bmp-parsing-vulnerability-in-syngo-fastview\/\"  data-wpil-monitor-id=\"41246\">vulnerability results from a leniency in h11&#8217;s parsing<\/a> of line terminators in chunked-coding message bodies. This flaw can lead to request smuggling <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2025-32829-sql-injection-vulnerability-in-telecontrol-server-basic\/\"  data-wpil-monitor-id=\"38725\">vulnerabilities when used with a buggy proxy server<\/a>. An attacker can exploit this <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2025-32824-critical-sql-injection-vulnerability-in-telecontrol-server-basic\/\"  data-wpil-monitor-id=\"38785\">vulnerability to inject<\/a> malicious payloads into the communication, leading to potential system compromise and data leakage.<\/p>\n<p><strong>Conceptual Example Code<\/strong><\/p><div id=\"ameeb-1497307757\" class=\"ameeb-content ameeb-entity-placement\"><div class=\"poptin-embedded\" data-id=\"f6b387694f681\"><\/div>\r\n\r\n\r\n\r\n\r\n\r\n<\/div>\n<p>Here&#8217;s a conceptual example of how an <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2025-3200-unauthenticated-remote-attacker-exploiting-insecure-tls-protocols\/\"  data-wpil-monitor-id=\"40805\">attacker might exploit<\/a> this vulnerability. Note that this is a simplified example and actual exploitation would require specific knowledge of the target <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2022-43110-critical-unauthenticated-remote-system-configuration-vulnerability-in-voltronic-power-viewpower-powershield-netguard\/\"  data-wpil-monitor-id=\"83131\">system and its configuration<\/a>.<\/p>\n<pre><code class=\"\" data-line=\"\">POST \/ HTTP\/1.1\nHost: target.example.com\nTransfer-Encoding: chunked\nContent-Length: 5\nG\nmalicious_payload\n0<\/code><\/pre>\n<p>In this example, the attacker is using a chunked transfer encoding to smuggle a malicious payload (&#8216;malicious_payload&#8217;) into the server communication. This payload could be code designed to exploit other <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2025-32843-sql-injection-vulnerability-in-telecontrol-server-basic-leading-to-authorization-bypass-and-data-manipulation\/\"  data-wpil-monitor-id=\"39069\">vulnerabilities in the system or to leak sensitive data<\/a>.<\/p>\n<p><strong>Mitigation<\/strong><\/p>\n<p>This <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2023-7224-openvpn-connect-vulnerability-in-macos-versions-3-0-to-3-4-6\/\"  data-wpil-monitor-id=\"41199\">vulnerability has been patched in h11 version<\/a> 0.16.0. Affected users should update to this version or later as soon as possible. If immediate patching is not feasible, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can provide temporary mitigation. These security measures may help detect and <a href=\"https:\/\/www.ameeba.com\/blog\/cve-2023-35989-integer-overflow-vulnerability-in-gtkwave-s-lxt2-zlib-block-allocation\/\"  data-wpil-monitor-id=\"41970\">block attempts to exploit this vulnerability<\/a>. However, they are not a substitute for applying the vendor patch and should only be considered as a temporary measure while the patching process is carried out.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Overview The cybersecurity community has recently identified a serious vulnerability in the h11 Python HTTP\/1.1 implementation. This flaw, recognized as CVE-2025-43859, has the potential to compromise systems and leak sensitive data under certain conditions. It&#8217;s a critical issue that mainly affects developers and organizations that use versions of h11 prior to 0.16.0 in conjunction with [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"footnotes":""},"categories":[1],"tags":[],"vendor":[],"product":[],"attack_vector":[],"asset_type":[],"severity":[],"exploit_status":[],"class_list":["post-34123","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/posts\/34123","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/comments?post=34123"}],"version-history":[{"count":10,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/posts\/34123\/revisions"}],"predecessor-version":[{"id":75669,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/posts\/34123\/revisions\/75669"}],"wp:attachment":[{"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/media?parent=34123"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/categories?post=34123"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/tags?post=34123"},{"taxonomy":"vendor","embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/vendor?post=34123"},{"taxonomy":"product","embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/product?post=34123"},{"taxonomy":"attack_vector","embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/attack_vector?post=34123"},{"taxonomy":"asset_type","embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/asset_type?post=34123"},{"taxonomy":"severity","embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/severity?post=34123"},{"taxonomy":"exploit_status","embeddable":true,"href":"https:\/\/www.ameeba.com\/blog\/wp-json\/wp\/v2\/exploit_status?post=34123"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}