Ubuntu Patches Seventeen Apache HTTP Server Flaws Including Remote Code Execution Risks
Canonical has published security notice USN-9016-1, a single update that closes seventeen separate vulnerabilities in the Apache HTTP Server packages shipped with Ubuntu. The affected estate is unusually broad: four of the issues (CVE-2026-46729, CVE-2026-47360, CVE-2026-48005 and CVE-2026-56153) reach back as far as Ubuntu 14.04 LTS and run through 16.04, 18.04, 20.04, 22.04, 24.04 and 26.04 LTS, while CVE-2026-56449 covers 20.04 LTS onward and a further eleven flaws affect Ubuntu 26.10 only. The impacts span the full range an administrator would worry about on a public web tier — denial of service, information disclosure, authentication bypass, access-control bypass, HTTP response smuggling and, in several cases, arbitrary code execution. Any Ubuntu host serving content through the apache2 package is in scope, including systems on the older LTS releases that are maintained through expanded security maintenance. Fixed packages are available for every affected release named in the notice.
The advisory does not publish exploitation details, proof-of-concept code or CVSS scores for any of the seventeen issues, so the mechanism is only described at the level Canonical gives it. The largest group is memory-handling errors: CVE-2026-46729, CVE-2026-56153 and CVE-2026-56449 all stem from the server mishandling certain memory operations, with the latter two capable of arbitrary code execution rather than a crash alone. Several flaws are module-specific — mod_rewrite mishandles memory during variable lookups (CVE-2026-56154), mod_http2 mishandles memory while processing HTTP/2 connections (CVE-2026-57941), and mod_ssl mishandles certain expressions in a way that allows intended access restrictions to be bypassed (CVE-2026-59797). A further cluster concerns how the server treats data it does not control: improper validation of FTP server responses can cause a forward proxy to connect to an arbitrary host (CVE-2026-63045), mishandled backend responses can trigger a denial of service (CVE-2026-63686), and misinterpreted backend responses enable HTTP response smuggling (CVE-2026-63718). The remainder cover authentication and WebDAV handling, including a Digest authentication validation failure exploitable by a machine-in-the-middle attacker (CVE-2026-73636), an authentication request management flaw causing denial of service (CVE-2026-73637), weak enforcement of access restrictions on user directories (CVE-2026-79768), exposure of WebDAV property information (CVE-2026-58415), and a WebDAV request-handling flaw that lets an authenticated user crash the service or corrupt property data (CVE-2026-93546). Session cookie handling is also at fault in CVE-2026-47360, which a remote attacker could use to leak sensitive information.
The strategic weight here comes from placement rather than from any single bug. Apache HTTP Server usually sits at the internet edge, terminating TLS and proxying to internal application servers, so a memory-corruption flaw reachable by an unauthenticated request is a direct path into that boundary, and the response smuggling and proxy-redirection issues let an attacker influence what sits behind it. The long tail of affected releases is its own exposure problem — organisations still running 14.04, 16.04 or 18.04 web servers are carrying four of these flaws on platforms that only receive fixes through extended maintenance, and inventory gaps on those hosts are common. On current exploitation status, FIRST EPSS data is available for twelve of the seventeen CVEs and all of them sit under one percent probability of exploitation in the next thirty days: CVE-2026-63292 is the highest at 0.9%, followed by CVE-2026-48005, CVE-2026-56449 and CVE-2026-57941 at 0.6%, CVE-2026-46729, CVE-2026-56153, CVE-2026-56154, CVE-2026-59797, CVE-2026-58415 and CVE-2026-63686 at 0.5%, and CVE-2026-47360 and CVE-2026-63045 at 0.4%. No exploitation data is published for the remaining five, and no in-the-wild activity is reported for any of them. That reads as a scheduled maintenance item rather than an incident, though the sheer breadth of modules touched — mod_ssl, mod_http2, mod_rewrite, mod_proxy, mod_dav and the authentication stack — means almost every Apache deployment on Ubuntu carries at least one of these defects somewhere in its enabled configuration.
Attack Surface
Web Application, Server OS, Infrastructure
Tactics
Initial Access, Impact, Defense Evasion, Credential Access
Techniques
- T1190 – Exploit Public-Facing Application
- T1499 – Endpoint Denial of Service
- T1211 – Exploitation for Defense Evasion
- T1557 – Adversary-in-the-Middle
SuperPRO's Threat Countermeasures Procedures
- Apply the apache2 package updates published in USN-9016-1 on every Ubuntu web server, using the update procedure the notice itself sets out for the affected releases, since those packages carry the fixes for the memory-corruption issues CVE-2026-56153 and CVE-2026-56449.
- Install the fixed apache2 package versions listed in USN-9016-1 for Ubuntu 14.04, 16.04 and 18.04 LTS, the releases where the notice addresses CVE-2026-46729, CVE-2026-47360, CVE-2026-48005 and CVE-2026-56153, noting that updates for those releases are published as expanded security maintenance builds.
- Scope exposure by identifying which Ubuntu hosts run the apache2 package and which of the modules named in USN-9016-1 are in use — mod_rewrite for CVE-2026-56154, mod_http2 for CVE-2026-57941, mod_ssl for CVE-2026-59797, the proxy handling behind CVE-2026-63045 and the WebDAV handling behind CVE-2026-58415 and CVE-2026-93546 — so remediation under the notice is ordered by which flaws actually apply.
- Install the fixed apache2 package versions listed in USN-9016-1 for Ubuntu 26.10, which is the only release the notice records as affected by the eleven additional flaws, among them CVE-2026-93546, CVE-2026-58415, CVE-2026-79768, CVE-2026-73636 and CVE-2026-73637.
- Install the fixed apache2 package versions listed in USN-9016-1 for Ubuntu 20.04, 22.04, 24.04 and 26.04 LTS, the releases the notice records as carrying CVE-2026-56449 alongside the four longer-standing issues CVE-2026-46729, CVE-2026-47360, CVE-2026-48005 and CVE-2026-56153.
- Follow the standard Ubuntu system update path the notice refers to for USN-9016-1 on every host running apache2, which moves the apache2, apache2-bin and apache2-utils packages to the fixed versions published for each supported release.
- Confirm per-host remediation by checking the installed apache2 package version against the fixed package version USN-9016-1 lists for that Ubuntu release, and cross-check the individual CVE entries the notice links in the Ubuntu CVE tracker for releases it marks as not affected.
