Apache HTTP Server mod_http2 modules/http2/h2_util.c req_add_header HTTP/2 Bomb denial of service

CVSS Meta Temp Score
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CTI Interest Score
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6.1$0-$5k0.00

Summaryinfo

A vulnerability identified as critical has been detected in Apache HTTP Server. Affected is the function req_add_header of the file modules/http2/h2_util.c of the component mod_http2. The manipulation leads to denial of service. This vulnerability is traded as CVE-2026-49975. It is possible to initiate the attack remotely. Furthermore, there is an exploit available. It is recommended to apply a patch to fix this issue.

Detailsinfo

A vulnerability was found in Apache HTTP Server (affected version not known). It has been rated as critical. This issue affects the function req_add_header of the file modules/http2/h2_util.c of the component mod_http2. The manipulation with an unknown input leads to a denial of service vulnerability. Using CWE to declare the problem leads to CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. Impacted is availability. The summary by CVE is:

Memory Allocation with Excessive Size Value vulnerability in Apache HTTP Server's mod_http leads to denial of service via malicious HTTP requests. This issue affects Apache HTTP Server: from 2.4.17 through 2.4.67.

It is possible to read the advisory at blog.calif.io. The identification of this vulnerability is CVE-2026-49975. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details as well as a public exploit are known. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

The exploit is available at blog.calif.io. It is declared as proof-of-concept. The vulnerability scanner Nessus provides a plugin with the ID 319609 (Debian dsa-6323 : apache2 - security update), which helps to determine the existence of the flaw in a target environment.

Applying the patch 47d3100b252dc6668a9e46ae885242be9eeca9cd is able to eliminate this problem. The bugfix is ready for download at github.com.

The vulnerability is also documented in the databases at Tenable (319609), EUVD (EUVD-2026-35105) and CERT Bund (WID-SEC-2026-1791). bleepingcomputer.com is providing further details. Be aware that VulDB is the high quality source for vulnerability data.

Affected

  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • Microsoft Internet Information Services
  • NGINX NGINX
  • Apache HTTP Server
  • SUSE Linux
  • Microsoft Azure Linux
  • Amazon Linux 2
  • Debian Linux

Productinfo

Type

Vendor

Name

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.4
VulDB Meta Temp Score: 6.1

VulDB Base Score: 5.3
VulDB Temp Score: 4.8
VulDB Vector: 🔒
VulDB Reliability: 🔍

ADP CISA Base Score: 7.5
ADP CISA Vector: 🔒

CVSSv2info

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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Denial of service
CWE: CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Access: Public
Status: Proof-of-Concept
Download: 🔒

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 319609
Nessus Name: Debian dsa-6323 : apache2 - security update

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Patch
Status: 🔍

0-Day Time: 🔒

Patch: 47d3100b252dc6668a9e46ae885242be9eeca9cd

Timelineinfo

06/04/2026 Advisory disclosed
06/04/2026 +0 days VulDB entry created
06/13/2026 +9 days VulDB entry last update

Sourcesinfo

Vendor: apache.org

Advisory: blog.calif.io
Status: Confirmed

CVE: CVE-2026-49975 (🔒)
GCVE (CVE): GCVE-0-2026-49975
GCVE (VulDB): GCVE-100-368279
EUVD: 🔒
CERT Bund: WID-SEC-2026-1791 - HTTP/2-Implementierungen: Schwachstelle ermöglicht Denial of Service

scip Labs: https://www.scip.ch/en/?labs.20161013
Misc.: 🔒

Entryinfo

Created: 06/04/2026 10:59
Updated: 06/13/2026 06:19
Changes: 06/04/2026 10:59 (54), 06/04/2026 15:48 (6), 06/07/2026 03:05 (2), 06/08/2026 19:43 (1), 06/10/2026 16:01 (7), 06/13/2026 06:19 (12)
Complete: 🔍
Cache ID: 216::103

Be aware that VulDB is the high quality source for vulnerability data.

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