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CVE Record

CVE-2026-42945: NGINX ngx_http_rewrite_module vulnerability

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.

CriticalCVSS 9.2Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

This is a critical NGINX rewrite-module flaw that can let unauthenticated internet traffic crash worker processes. Under weaker memory-protection conditions, code execution is also described. The risk is highest for public NGINX systems using the specific rewrite configuration pattern described by F5/CVE sources.

Executive priority

Treat as urgent for internet-facing NGINX systems, especially reverse proxies and edge gateways. Prioritize inventory and patching, then configuration review. The business impact is service disruption, with potential code execution in weaker ASLR conditions.

Technical view

The flaw is a heap buffer overflow in ngx_http_rewrite_module. It requires a rewrite directive followed by rewrite, if, or set, using unnamed PCRE captures such as $1 with a replacement string containing ?. Triggering requires crafted HTTP requests and conditions beyond attacker control.

Likely exposure

Exposure is likely limited to NGINX deployments using the vulnerable rewrite-module configuration pattern. The bundle identifies NGINX Plus R37, R36, and R32, and NGINX Open Source metadata spanning 0.6.27 to 1.31.0, but some status details are incomplete or ambiguous.

Exploitation context

The bundle says unauthenticated network attackers can cause worker restarts and may execute code if ASLR is disabled or bypassed. It does not cite CISA KEV listing or confirmed active exploitation. Public research links exist, so defenders should assume technical details are available.

Researcher notes

The vulnerability depends on a narrow rewrite-module configuration and crafted requests. CVSS 4.0 is 9.2 with high attack complexity. The source bundle does not prove active exploitation, and EoTS versions were not evaluated.

Mitigation direction

  • Review F5 advisory K000161019 and apply vendor-supported fixes.
  • Apply relevant Red Hat errata where Red Hat packages are used.
  • Inventory public NGINX Plus and Open Source instances first.
  • Review rewrite rules for the documented capture and question-mark pattern.
  • Keep ASLR enabled on affected systems.
  • Monitor NGINX worker crashes until fixes are confirmed.

Validation and detection

  • Check deployed NGINX versions against F5 and Red Hat guidance.
  • Inspect nginx configuration for rewrite followed by rewrite, if, or set.
  • Search rewrite replacements using unnamed captures such as $1 or $2.
  • Confirm whether replacement strings include a question mark.
  • Verify package updates from the relevant vendor advisory are installed.
  • Review logs for unexplained NGINX worker process restarts.
Prepared
Confidence
medium
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-122: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cwe · low confidence lookup

CWE-131: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-42945 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.2 (4.0)
Known Exploited
No
Published

Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

3CVSS vectors
5Timeline events
3ADP providers
34Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

3 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.2CVSS 4.0CriticalCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N——f5
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9f5
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9redhat-SADP

Vulnerability scoring details

Base CVSS 4.0 score

9.2Critical
CVSS 4.0 vector shape for CVE-2026-42945Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container
redhat-SADPnginx: NGINX: Arbitrary Code Execution Vulnerability
other:Red Hat severity ratingcvssV3_1
  • 2026-05-13T16:04:29.017Z: Reported to Red Hat.
  • 2026-05-13T14:12:43.971Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
F5NGINX PlusR37, R36, R32unknown
F5NGINX Open Source1.31.0, 0.6.27unaffected
Weakness

CWE details

CWE-122CWE-131

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.