What is CVE-2026-42533?

CVE-2026-42533 is NGINX Map directive and Regex matching vulnerability. The supplied enrichment data classifies it as Memory Corruption mapped to CWE-122 Heap-based Buffer Overflow.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Exploitation is reported, but no independent confirmation is available in the sources we have. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-42533 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

14 public PoC repositories reported; 3 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-42533 using CVSS 8.1, EPSS 4%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

The supplied mitigation guidance says to apply vendor patches and restrict external exposure until fixed. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

highMemory Corruptionpublic exploit

CVE-2026-42533

CVE-2026-42533 — NGINX Map directive and Regex matching vulnerability

A vulnerability exists in NGINX Plus and NGINX Open Source when a map directive uses regex matching and a string expression references the map's regex capture variables before referencing the map output variable. Alternatively, the same result could be achieved by using a non-cacheable variable in a string expression under certain conditions. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Impact: This vulnerability may allow remote attackers to cause a denial-of-service (DoS) on the NGINX system or to possibly trigger a code execution. 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.

Published Jul 15, 2026Updated Aug 10, 2026Sources: NVD, F5 (CNA), Red Hat (VEX), SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Reported

not confirmed by CISA

EPSS

ahead of 91% of scored CVEs

Affects

5 products listed

CVSS base

8.1

high · 3 sources

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

PoC

none · proof-of-concept · active

Automatable

can an attacker script all four kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

The vendor's own words where we have them.

Upgrade NGINX Plus to a fixed release. Apply vendor patches per advisory and restrict external exposure of the affected component until patched.

Red Hat VEX · CVE-2026-42533

fixed4affected55not affected1

vendor_fix: For details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/

workaround: To mitigate this vulnerability, do not use unnamed captures. Use named captures instead and only use them in the same block with the regex match. Red Hat recommends updating nginx…

none_available: Affected

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
F5	NGINX Plus	37.0.0.1 to < 37.0.3.1	Vulnerable
F5	NGINX Plus	R36	Vulnerable
F5	NGINX Plus	R33	Vulnerable
F5	NGINX Open Source	1.31.2 to < 1.31.3	Vulnerable
F5	NGINX Open Source	0.9.6 to < 1.30.4	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Availability

High

Confidentiality

High

Integrity

High

Scope

Unchanged

Attack Complexity

High

Attack Vector

Network

Privileges Req

None

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
8.1	CVSS 3.1	high	2.2	5.9	f5.com (CNA), F5 (CNA)
9.2	CVSS 4.0	critical	—	—	F5 (CNA)
7	CVSS 3.1	high	—	—	Red Hat (VEX)

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

What this weakness leads to

MITRE's own consequences and mitigations for the weakness class — the authority's wording, not guidance derived from the CVSS vector.

MITRE

CWE-122 · Heap-based Buffer Overflow

DoS: Crash, Exit, or Restart
DoS: Resource Consumption (CPU)
DoS: Resource Consumption (Memory)
Execute Unauthorized Code or Commands

Mitigation: Pre-design: Use a language or compiler that performs automatic bounds checking.

Weakness & attack patterns

CWE-122Heap-based Buffer Overflow

Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.

CAPEC-92 · Forced Integer Overflow

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

3 of the 5 sampled are weaponized

Exploit entries

Exploit-DB and CTI exploit indexes

Social mentions

Posts naming this CVE. Attention, not evidence of exploitation — it spikes on disclosure and decays whether or not anything is exploited.

35 more posts on this CVEShowing 5 of 40 · Who is discussing this CVE, and how loudlyUnlock free

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Prioritize edge telemetry for network-reachable NGINX Plus, NGINX Open Source.
Monitor for scanner or exploit-pattern traffic after 14 public PoC repositories were reported.

web/proxy/WAF logsapplication logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 8.1 (AV:N)
Aug 10, 2026 · NVD
Cve is exploited 0xCyberstan/CVE-2026-42533-POC
Aug 6, 2026 · SOCRadar CTI
Cve is exploited imbas007/CVE-2026-42533
Jul 27, 2026 · SOCRadar CTI
Initial · CVE published
Jul 15, 2026 · NVD

Source activity

Readings a source repeats on a schedule, counted rather than listed.

13×SVRS was changedJul 20, 2026 – Aug 22, 2026 · SOCRadar CTI
13×TweetsJul 21, 2026 – Aug 18, 2026 · SOCRadar CTI
10×Github ReposJul 20, 2026 – Aug 29, 2026 · SOCRadar CTI
2×1 time mentioned on 1 Telegram channelJul 22, 2026 – Jul 28, 2026 · SOCRadar CTI

References

6 on the record

my.f5.com/manage/s/article/K000162097
Vendor Advisory, NIST
access.redhat.com/errata/RHSA-2026:46012
Vendor Advisory
access.redhat.com/security/cve/CVE-2026-42533
Vendor Advisory
bugzilla.redhat.com/show_bug.cgi?id=2500967
Vendor Advisory
www.cve.org/CVERecord?id=CVE-2026-42533
Vendor Advisory
nvd.nist.gov/vuln/detail/CVE-2026-42533
NVD

Coverage

19 stories from the feeds we poll

14 more reports on this CVEShowing 5 of 19 · Vendor research and security press coverageUnlock free

Elsewhere on this site

F5every CVE for this vendor
Memory Corruptionsame class
CWE-122other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-42533 is NGINX Map directive and Regex matching vulnerability, a high vulnerability affecting NGINX Plus, NGINX Open Source from F5. The current evidence does not list it in CISA KEV, and the exploit status is: Exploitation is reported, but no independent confirmation is available in the sources we have. Public exploit evidence is: 14 public PoC repositories reported; 3 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 8.1 describes technical severity, while EPSS 4% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.