CVE-2026-57941
Description
A flaw was found in the mod_http2 module of Apache HTTP Server. A remote, unauthenticated attacker could exploit a use-after-free condition—where memory is accessed after being released—through re-entrant processing of shared session buffers. This flaw can allow an attacker to potentially execute arbitrary code or crash the server, resulting in a Denial of Service (DoS).
Statement
A use-after-free flaw was found in mod_http2, the HTTP/2 module for the Apache HTTP Server. A remote attacker with no privileges can trigger re-entrant use of a shared per-session buffer (session->bbtmp) while the server is handling HTTP/2 traffic. That interleaving is not a single reliable request, and the demonstrated effect is a crash of the httpd worker, which is a denial of service. A further memory-corruption outcome has not been shown.
Mitigation
Disable mod_http2 until a fixed package is installed. In /etc/httpd/conf.modules.d/10-h2.conf, comment out the module and restart the service:
#LoadModule http2_module modules/mod_http2.so
$ systemctl restart httpd
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7 | N/A | 9.8 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | Low | N/A | High |
| Integrity Impact | Low | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
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