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CVE-2026-42945

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_rewrite_module module. This vulnerability exists when the rewrite directive is followed by a rewrite, if, or set directive and an unnamed Perl-Compatible Regular Expression (PCRE) capture (for example, $1, $2) with a replacement string that includes a question mark (?). An unauthenticated attacker along with conditions beyond its 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. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

CVSS
8.1High
Exploited in the wild
Not knownUnvetted proof-of-concept code on GitHub; not in CISA KEV
EPSS
68.0%chance of exploitation in the next 30 daystop 0.7% of scored CVEsFIRST score of 11 Nov 2026
Fix
Fixed in >= 1.31.0 and < *, >= R37 and < *per the vendor
Published
13 May 2026analysed here 12 Nov 2026

Do first. Upgrade to a fixed release: >= 1.31.0 and < *, >= R37 and < *.

Summary

Triage

Attack surface
Server-side
Exploitable
At runtime
Attack vector
network
Weaknesses
Can a WAF block it?
Partly. See why

The summary, impact and action text on this page are written by our AI analysis pipeline, or taken from the NVD description when a CVE was imported from NVD. They are not the vendor's wording: check them against the sources. A longer AI executive summary and technical analysis are generated for signed-in accounts on the Max plan.

Affected products

ProductAffected versions
F5 NGINX Open Source>= 0.6.27 and < 1.30.1Vendor says fixed in: >= 1.31.0 and < *
F5 NGINX Plus>= R36 and < R36 P4>= R32 and < R32 P6Vendor says fixed in: >= R37 and < *

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

Products named in our analysis

  • f5:dos
  • f5:nginx_gateway_fabric
  • f5:nginx_ingress_controller
  • f5:nginx_instance_manager
  • f5:nginx_open_source
  • f5:nginx_plus
  • f5:waf

Fix and mitigation

WAF and other mitigations

Can a WAF block it? Partly. Cloudflare publishes WAF rules written for this CVE. Such rules block the known exploit requests and buy time, but attackers can change the request to get past them, so they do not replace the patch.

Also consider: patch · enable the vendor rule in block mode

Based on WAF vendor rules published for this CVE. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.

Remediation steps (AI-written)

Step-by-step remediation is generated for accounts on the Max plan, for CVEs that match a technology in their stack. Add this technology to your stack to see the fix checklist.

Exploitation evidence

CISA KEV catalog
Not listed as of our last sync.
Public exploit code
Unvetted proof-of-concept code on GitHub: 48 GitHub proofs of concept
CISA SSVC
exploitation none, automatable no, technical impact totalAssessed by CISA 13 May 2026 (SSVC 2.0.3). Exploitation is none, poc (public proof of concept) or active.

GitHub proofs of concept

and 44 more repositories

Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.

Timeline

  1. 13 May 2026CISA SSVC assessment: exploitation none
  2. 13 May 2026Published1 day later
  3. 14 May 2026First proof-of-concept repository on GitHub (unvetted)same day later
  4. 10 Sept 2026CVE record last updated120 days (about 4 months) later
  5. 12 Nov 2026Analysed by vulneraibility.com63 days (about 2 months) later

CVSS vector

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

MetricValueWhat it means
Attack vectorNetworkReachable over the internet or any routable network.
Attack complexityHighNeeds specific conditions, a race or a particular configuration.
Privileges requiredNoneThe attacker needs no prior access.
User interactionNoneNo victim action needed.
ScopeUnchangedImpact stays within the vulnerable component.
ConfidentialityHighTotal data disclosure possible.
IntegrityHighComplete modification possible.
AvailabilityHighFull outage possible.

Common questions

Is CVE-2026-42945 being exploited?

Not confirmed. CVE-2026-42945 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 68% probability of exploitation in the next 30 days.

How severe is CVE-2026-42945?

CVE-2026-42945 is rated High with a CVSS score of 8.1. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2026-42945?

Yes. A fix has been recorded for CVE-2026-42945. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2026-42945 affect?

CVE-2026-42945 affects f5:dos, f5:nginx_gateway_fabric, f5:nginx_ingress_controller, f5:nginx_instance_manager, and 3 further products or versions. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

References

NVDCVE.orgCVE DetailsSource

34 references in the CVE record, grouped by the tags the record gives them.

Advisories (28)

Show 22 more

Patches (1)

Other links (5)

Where the data on this page comes from

Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.

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