Apache HTTP Server: Heap-based Buffer Overflow
CVE-2026-28780 is a high-severity heap-based buffer overflow vulnerability in Apache HTTP Server from Apache, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Apache HTTP Server versions: 2.4.66 and earlier. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 1.38% chance of exploitation within 30 days, higher than 73% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update HTTP Server to 2.4.67 or a later version.
- Read the advisory on httpd.apache.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | CISA (ADP) |
| CVSS 3.1 | 8.1 | High | CNA |
Official description
Heap-based Buffer Overflow vulnerability in mod_proxy_ajp of Apache HTTP Server. If mod_proxy_ajp connects to a malicious AJP server this AJP server can send a malicious AJP message back to mod_proxy_ajp and cause it to write 4 attacker controlled bytes after the end of a heap based buffer. This issue affects Apache HTTP Server: through 2.4.66. Users are recommended to upgrade to version 2.4.67, which fixes the issue.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Heap-based Buffer Overflow
The product writes past the end of a buffer that was allocated on the heap.
How developers prevent this class of flaw
- Pre-design: Use a language or compiler that performs automatic bounds checking.
- Use an abstraction library to abstract away risky APIs. Not a complete solution.
- Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- httpd.apache.org/security/vulnerabilities_24.htmlRelease Notes
Third-party and government advisories
- openwall.com/lists/oss-security/2026/05/05/9Mailing List, Third Party Advisory
Other references
- access.redhat.com/errata/RHSA-2026:21391
- access.redhat.com/errata/RHSA-2026:21433
- access.redhat.com/errata/RHSA-2026:22140
- access.redhat.com/errata/RHSA-2026:27200
- access.redhat.com/errata/RHSA-2026:27201
- access.redhat.com/errata/RHSA-2026:36373
- access.redhat.com/errata/RHSA-2026:36831
- access.redhat.com/errata/RHSA-2026:36846
- access.redhat.com/errata/RHSA-2026:47046
- access.redhat.com/errata/RHSA-2026:62165
- access.redhat.com/errata/RHSA-2026:66323
- access.redhat.com/errata/RHSA-2026:67152
- access.redhat.com/security/cve/CVE-2026-28780
- bugzilla.redhat.com/show_bug.cgi?id=2466913
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-28780.json
Other vulnerabilities in Apache HTTP Server
- 8.1 High severity
- 8.8 High severity
- 7.3 High severity
- 8.1 High severity
- 7.5 High severity
- 7.5 High severity
Recent Heap-based Buffer Overflow vulnerabilities
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.1 High severity
- 8.1 High severity
- 8.1 High severity
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