Out-of-bounds Read in Apache HTTP Server merge_response_headers
CVE-2026-43951 is a moderate-severity out-of-bounds read vulnerability in Apache HTTP Server affecting versions 2.4.0 through 2.4.67. The flaw is in the merge_response_headers processing path and occurs when mod_headers and mod_mime are used together in configurations involving multiple response languages. Apache states that the bug can cause child process crashes. The issue was fixed in the 2.4.x branch by revision r1935006 and is addressed in Apache HTTP Server 2.4.68.
Are you exposed to this one?
Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.
Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
mod_headers and mod_mime in configurations that use multiple response languages, but the authoritative remediation is to upgrade.Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
8 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An out-of-bounds read vulnerability in Apache HTTP Server merge_response_headers involving mod_headers and mod_mime that can cause child process crashes.
Apache HTTP Server vulnerability affecting mod_headers and mod_mime, fixed in 2.4.68; exact impact is unclear due to encoding issues.
Apache HTTP Server vulnerability involving header handling due to incorrect interaction between mod_headers and mod_mime.
An out-of-bounds read vulnerability in Apache HTTP Server involving mod_headers and mod_mime with multiple response languages, potentially causing a crash.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.