VulnerabilityPublished 24 Mar 2026

CVE-2026-28755: F5 NGINX Open Source · Incorrect Authorization

Affects F5 NGINX Open SourceSource CVE Database V5

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Not known to be exploited · CVSS 5.4 Medium : upgrade to 1.29.7 or 1.28.3 when convenient.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

5.4Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 3% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.29.7, 1.28.3

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 24 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
Public exploit code: GitHub proofs of concept
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), GitHub proofs of concept, the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade F5 NGINX Open Source to 1.29.7 or 1.28.3.

Affected software

Product	Affected	Fixed in
F5NGINX Open Source	Affected >=1.29.0 <1.29.7	Fixed in 1.29.7
F5NGINX Open Source	Affected >=1.27.2 <1.28.3	Fixed in 1.28.3
F5NGINX Plus	Affected >=R34 >=R33 =R36 =R35	Fixed in–

AI-suggested

To mitigate CVE-2026-28755, organizations should: 1) Upgrade affected NGINX Open Source versions (1.27.2 and 1.29.0) to patched releases once available from F5 or the NGINX project. 2) Temporarily disable ssl_ocsp or ssl_verify_client if immediate patching is not possible, understanding this reduces security and should be a short-term measure. 3) Implement additional layers of client authentication or authorization beyond TLS client certificates, such as application-level access controls or multi-factor authentication. 4) Monitor TLS handshake logs for connections using revoked certificates or unusual client certificate usage patterns. 5) Use OCSP stapling on the server side to improve revocation checking reliability and consider alternative revocation mechanisms like CRLs if feasible. 6) Restrict network access to NGINX servers requiring client certificates to trusted networks or VPNs to reduce exposure. 7) Conduct regular audits of client certificates and revoke any that are no longer needed or compromised. These steps help reduce the risk of unauthorized access while awaiting official patches.

Description

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_stream_ssl_module module due to the improper handling of revoked certificates when configured with the ssl_verify_client on and ssl_ocsp on directives, allowing the TLS handshake to succeed even after an OCSP check identifies the certificate as revoked. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Impact

The primary impact of CVE-2026-28755 is the potential unauthorized access to systems that rely on client certificate authentication with OCSP revocation checking enabled. Attackers possessing revoked certificates can bypass revocation checks and successfully complete TLS handshakes, potentially gaining access to protected resources or services. This undermines the integrity of the authentication process and could lead to data exposure or unauthorized command execution depending on the application context. Although the vulnerability does not affect availability, the compromise of confidentiality and integrity can have serious consequences in environments requiring strong client authentication, such as financial services, government agencies, and critical infrastructure. Organizations using NGINX as a TLS termination point with client certificate validation are at risk, especially if they rely on OCSP for revocation checking. The moderate CVSS score reflects the need for privileged access to present a revoked certificate but highlights the risk of bypassing a critical security control. The absence of known exploits reduces immediate risk but does not eliminate the threat of future exploitation.

CWE-863Incorrect Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #17OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Architecture and Design
Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

my.f5.com/manage/s/article/K000160368 (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 24 Mar 2026, 15:07 UTC

Public exploits and detectionGitHub proofs of concept

WeaknessesCWE-863

Technical details

References

Community reviews

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