Vulnerability-Lookup

RHSA-2026:25057

Vulnerability from csaf_redhat - Published: 2026-06-10 11:31 - Updated: 2026-06-10 21:22

Summary

Red Hat Security Advisory: mod_http2 security update

Severity

Important

Notes

Topic: An update for mod_http2 is now available for Red Hat Enterprise Linux 9. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

Details: The mod_h2 Apache httpd module implements the HTTP2 protocol (h2+h2c) on top of libnghttp2 for httpd 2.4 servers. Security Fix(es): * httpd: HTTP/2: Remote Denial of Service via compression bomb and Slowloris-style attack (CVE-2026-49975) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Terms of Use: This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original.

CVE-2026-49975

A flaw was found in HTTP/2, affecting various web servers. A remote attacker can exploit this vulnerability by combining an HPACK compression bomb with a zero-byte flow-control window. This technique allows a small amount of data to expand into large memory allocations on the server, which are then held, leading to a denial of service (DoS) by rendering the server inaccessible.

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE-409 - Improper Handling of Highly Compressed Data (Data Amplification)

Affected products

Fixed 13 products

Product	Version	Remediation
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-0:2.0.26-6.el9_8.1.aarch64	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-0:2.0.26-6.el9_8.1.ppc64le	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-0:2.0.26-6.el9_8.1.s390x	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-0:2.0.26-6.el9_8.1.src	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-0:2.0.26-6.el9_8.1.x86_64	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-debuginfo-0:2.0.26-6.el9_8.1.aarch64	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-debuginfo-0:2.0.26-6.el9_8.1.ppc64le	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-debuginfo-0:2.0.26-6.el9_8.1.s390x	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-debuginfo-0:2.0.26-6.el9_8.1.x86_64	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-debugsource-0:2.0.26-6.el9_8.1.aarch64	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-debugsource-0:2.0.26-6.el9_8.1.ppc64le	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-debugsource-0:2.0.26-6.el9_8.1.s390x	—	Vendor Fix fix Workaround
Unresolved product id: AppStream-9.8.0.Z.MAIN.EUS:mod_http2-debugsource-0:2.0.26-6.el9_8.1.x86_64	—	Vendor Fix fix Workaround

Threats

Impact Important

References

10 references

URL	Category
https://access.redhat.com/errata/RHSA-2026:25057	self
https://access.redhat.com/security/updates/classi…	external
https://bugzilla.redhat.com/show_bug.cgi?id=2485371	external
https://security.access.redhat.com/data/csaf/v2/a…	self
https://access.redhat.com/security/cve/CVE-2026-49975	self
https://bugzilla.redhat.com/show_bug.cgi?id=2485371	external
https://access.redhat.com/security/vulnerabilitie…	external
https://www.cve.org/CVERecord?id=CVE-2026-49975	external
https://nvd.nist.gov/vuln/detail/CVE-2026-49975	external
https://blog.calif.io/p/codex-discovered-a-hidden…	external

JSON

To clipboard

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          "name": "mod_http2-debugsource-0:2.0.26-6.el9_8.1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 9)",
          "product_id": "AppStream-9.8.0.Z.MAIN.EUS:mod_http2-debugsource-0:2.0.26-6.el9_8.1.s390x"
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        "product_reference": "mod_http2-debugsource-0:2.0.26-6.el9_8.1.s390x",
        "relates_to_product_reference": "AppStream-9.8.0.Z.MAIN.EUS"
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        "full_product_name": {
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        "product_reference": "mod_http2-debugsource-0:2.0.26-6.el9_8.1.x86_64",
        "relates_to_product_reference": "AppStream-9.8.0.Z.MAIN.EUS"
      }
    ]
  },
  "vulnerabilities": [
    {
      "cve": "CVE-2026-49975",
      "cwe": {
        "id": "CWE-409",
        "name": "Improper Handling of Highly Compressed Data (Data Amplification)"
      },
      "discovery_date": "2026-06-05T06:04:44.009000+00:00",
      "ids": [
        {
          "system_name": "Red Hat Bugzilla ID",
          "text": "2485371"
        }
      ],
      "notes": [
        {
          "category": "description",
          "text": "A flaw was found in HTTP/2, affecting various web servers. A remote attacker can exploit this vulnerability by combining an HPACK compression bomb with a zero-byte flow-control window. This technique allows a small amount of data to expand into large memory allocations on the server, which are then held, leading to a denial of service (DoS) by rendering the server inaccessible.",
          "title": "Vulnerability description"
        },
        {
          "category": "summary",
          "text": "httpd: HTTP/2: Remote Denial of Service via compression bomb and Slowloris-style attack",
          "title": "Vulnerability summary"
        },
        {
          "category": "other",
          "text": "The Apache\u0027s `httpd` HTTP/2 protocol implementation has a denial-of-service (DoS) vulnerability that is rated as Important. An unauthenticated remote attacker can exploit this flaw by combining HPACK compression with flow control manipulation, leading to significant server memory exhaustion and rendering the service inaccessible. This vulnerability exists in default HTTP/2 configurations.",
          "title": "Statement"
        },
        {
          "category": "general",
          "text": "The CVSS score(s) listed for this vulnerability do not reflect the associated product\u0027s status, and are included for informational purposes to better understand the severity of this vulnerability.",
          "title": "CVSS score applicability"
        }
      ],
      "product_status": {
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          "summary": "Canonical URL",
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        },
        {
          "category": "external",
          "summary": "RHBZ#2485371",
          "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2485371"
        },
        {
          "category": "external",
          "summary": "RHSB-2026-007",
          "url": "https://access.redhat.com/security/vulnerabilities/RHSB-2026-007"
        },
        {
          "category": "external",
          "summary": "https://www.cve.org/CVERecord?id=CVE-2026-49975",
          "url": "https://www.cve.org/CVERecord?id=CVE-2026-49975"
        },
        {
          "category": "external",
          "summary": "https://nvd.nist.gov/vuln/detail/CVE-2026-49975",
          "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49975"
        },
        {
          "category": "external",
          "summary": "https://blog.calif.io/p/codex-discovered-a-hidden-http2-bomb",
          "url": "https://blog.calif.io/p/codex-discovered-a-hidden-http2-bomb"
        }
      ],
      "release_date": "2026-06-03T00:00:00+00:00",
      "remediations": [
        {
          "category": "vendor_fix",
          "date": "2026-06-10T11:31:57+00:00",
          "details": "For details on how to apply this update, which includes the changes described in this advisory, refer to:\n\nhttps://access.redhat.com/articles/11258",
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          ],
          "restart_required": {
            "category": "none"
          },
          "url": "https://access.redhat.com/errata/RHSA-2026:25057"
        },
        {
          "category": "workaround",
          "details": "See the security bulletin for a detailed mitigation procedure.",
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            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
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          ]
        }
      ],
      "threats": [
        {
          "category": "impact",
          "details": "Important"
        }
      ],
      "title": "httpd: HTTP/2: Remote Denial of Service via compression bomb and Slowloris-style attack"
    }
  ]
}

CVE-2026-49975 (GCVE-0-2026-49975)

Vulnerability from cvelistv5 – Published: 2026-06-08 15:26 – Updated: 2026-06-09 15:25

Title

Apache HTTP Server: mod_http2 denial of service

Summary

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.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-789 - Memory Allocation with Excessive Size Value

Assigner

apache

References

4 references

URL	Tags
https://httpd.apache.org/security/vulnerabilities…	vendor-advisory
http://www.openwall.com/lists/oss-security/2026/06/03/3
https://lists.debian.org/debian-lts-announce/2026…
http://www.openwall.com/lists/oss-security/2026/0…

Impacted products

1 product

Vendor	Product	Version
Apache Software Foundation	Apache HTTP Server	Affected: 2.4.17 , ≤ 2.4.67 (semver)

Credits

Quang Luong of Calif.IO in collaboration with OpenAI Codex

Show details on NVD website

JSON

To clipboard

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          },
          {
            "url": "https://lists.debian.org/debian-lts-announce/2026/06/msg00009.html"
          },
          {
            "url": "http://www.openwall.com/lists/oss-security/2026/06/08/16"
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                ],
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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

RHSA-2026:25057

CVE-2026-49975 (GCVE-0-2026-49975)

Tags

Sightings

Nomenclature