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Highest advisory severityHigh 2 vendors · 2 advisories

CVE-2026-56434

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssi_module module

CVE-2026-56434: NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssi_module module. Not in the CISA KEV catalog.

Compare the source-linked records below. Ratings and product/version details belong to each advisory; they are not a single CVE-wide score or proof that every listed product is affected. How VulniPulse collects and checks evidence.

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CVE-2026-56434 key facts

CISA KEV
Not listed (catalog checked )
Highest advisory severity
High
CVSS base score
8.3 (F5), 6.5 (Red Hat)
CVSS vector
  • CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H (Red Hat)
Weakness
CWE-125
Fixed releases
  • F5: 37.0.3.1, R36 P7, 1.31.3, 1.30.4
  • Red Hat: nginx-2:1.26.3-6.el10_2.6, nginx:1.24-8100020260809162034.489197e6, nginx-2:1.20.1-28.el9_8.5, nginx:1.24-9080020260804072754.9, nginx:1.26-9080020260803214158.9, discovery/discovery-ui-rhel9:1788206196 and 12 more in the advisory
Vendor advisories
2 from F5, Red Hat
VulniPulse record
Published · Updated

Scores, vectors, weaknesses and fixed releases are quoted from vendor advisories that cover only CVE-2026-56434; bulletin-wide values are not repeated here.

Is CVE-2026-56434 exploited?

No exploitation is reported in the sources VulniPulse tracks: CVE-2026-56434 is not in the CISA KEV catalog (checked ) and no tracked advisory for it reports exploitation. That is not proof the vulnerability cannot be exploited.

How do I fix CVE-2026-56434?

Upgrade to a fixed release named by the vendor:

  • F5: 37.0.3.1, R36 P7, 1.31.3, 1.30.4
  • Red Hat: nginx-2:1.26.3-6.el10_2.6, nginx:1.24-8100020260809162034.489197e6, nginx-2:1.20.1-28.el9_8.5, nginx:1.24-9080020260804072754.9, nginx:1.26-9080020260803214158.9, discovery/discovery-ui-rhel9:1788206196
  • To prevent exploitation, avoid configuring NGINX with `ngx_http_ssi_module` when `proxy_pass` and `proxy_buffering off` are simultaneously active. If Server-Side Includes (SSI) are not essential, disable the `ngx_http_ssi_module` by removing or commenting out the `ssi on;` directive. Alternatively, ensure `proxy_buffering` is explicitly enabled (`proxy_buffering on;`) when `proxy_pass` is used with SSI. A reload or restart of the NGINX service is necessary for configuration changes to apply, which may cause a brief service interruption. (Red Hat)

Vendor advisory comparison

F5

1 advisory
  • Advisory severityHigh8.3

    High [CVE-2026-56434] NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssi_module module

    CVE-2026-56434Source published Source updated

    NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssi_module module. This vulnerability may exist when the Server-Side Includes (SSI), proxy_pass, and proxy_buffering off directives are configured. With this configuration, an unauthenticated attacker with man-in-the-middle (MITM) ability to control responses from an upstream server may be able to cause a use-after-free in the NGINX worker process. This issue may lead to limited modification of memory or a restart of the NGINX worker process. Impact: There is no control plane exposure; this is a data plane issue only. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

    Affected products in this advisory
    • NGINX Plus
    • NGINX Open Source
    Source-reported affected versions
    • NGINX Plus 37.0.0.1 before 37.0.3.1
    • NGINX Plus R36 before R36 P7
    • NGINX Plus R33
    • NGINX Open Source 1.31.2 before 1.31.3

    1 more entries in the full advisory.

    Source-reported fixed versions
    • 37.0.3.1
    • R36 P7
    • 1.31.3
    • 1.30.4
    Mitigation guidance
    No mitigation guidance extracted; consult the source.
    Full advisory and evidenceOpen source bulletin

Red Hat

1 advisory
  • Advisory severityMedium6.5

    Medium [CVE-2026-56434] Heap buffer over-read allows memory modification or denial of service

    CVE-2026-56434Source published Source updated

    NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_ssi_module module. This vulnerability may exist when the Server-Side Includes (SSI), proxy_pass, and proxy_buffering off directives are configured. With this configuration, an unauthenticated attacker with man-in-the-middle (MITM) ability to control responses from an upstream server may be able to cause a use-after-free in the NGINX worker process. This issue may lead to limited modification of memory or a restart of the NGINX worker process. There is no control plane exposure; this is a data plane issue only. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated. A vulnerability in NGINX's ngx_http_ssi_module allows an unauthenticated MITM attacker to trigger a heap buffer…

    Affected products in this advisory
    • Red Hat Enterprise Linux 10
    • Red Hat Enterprise Linux 8
    • Red Hat Enterprise Linux 9
    • Red Hat Discovery 2

    4 more entries in the full advisory.

    Source-reported affected versions
    Affected-version details not available in this record.
    Source-reported fixed versions
    • nginx-2:1.26.3-6.el10_2.6
    • nginx:1.24-8100020260809162034.489197e6
    • nginx-2:1.20.1-28.el9_8.5
    • nginx:1.24-9080020260804072754.9

    14 more entries in the full advisory.

    Mitigation guidance
    • To prevent exploitation, avoid configuring NGINX with `ngx_http_ssi_module` when `proxy_pass` and `proxy_buffering off` are simultaneously active. If Server-Side Includes (SSI) are not essential, disable the `ngx_http_ssi_module` by removing or commenting out the `ssi on;` directive. Alternatively, ensure `proxy_buffering` is explicitly enabled (`proxy_buffering on;`) when `proxy_pass` is used with SSI. A reload or restart of the NGINX service is necessary for configuration changes to apply, which may cause a brief service interruption.
    Full advisory and evidenceOpen source bulletin

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