Medium Memory corruption

CVE-2026-42934 — NGINX ngx_http_charset_module vulnerability

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_charset_module module. When charset, source_charset, and charset_map and proxy_pass with disabled buffering ("off") directives are configured, unauthenticated attackers can send requests that with conditions beyond the attackers' control to cause a heap buffer over-read in the NGINX worker process, leading to limited disclosure of memory or a restart. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Published May 13, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: f5

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.7% (30-day exploitation probability)+8
Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

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

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.73%

ahead of 53% of scored CVEs · Oct 14, 2026

Affects

Dos and 6 more

CVSS base

4.8

Medium · 2 source(s)

CISA SSVC assessment CISA

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

Exploitation

None

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented mitigation — my.f5.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (F5 Dos, F5 Nginx Gateway Fabric, F5 Nginx Ingress Controller…).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
Apply the documented mitigations until a definitive fix is available.
Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
F5	Dos	version 4.8.0≥ 4.3.0 and ≤ 4.7.0	Vulnerable	NIST National Vulnerability Database
F5	Nginx Gateway Fabric	≥ 2.0.0 and ≤ 2.6.0≥ 1.3.0 and ≤ 1.6.2	Vulnerable	NIST National Vulnerability Database
F5	Nginx Ingress Controller	≥ 4.0.0 and ≤ 4.0.1≥ 5.0.0 and ≤ 5.4.2≥ 3.5.0 and ≤ 3.7.2	Vulnerable	NIST National Vulnerability Database
F5	Nginx Instance Manager	≥ 2.16.0 and ≤ 2.22.0	Vulnerable	NIST National Vulnerability Database
F5	Nginx Open Source	≥ 0.3.50 and < 1.30.1	Vulnerable	CVE Program (cve.org) e CISA ADP
F5	Nginx Open Source	≥ 1.0.0 and ≤ 1.30.0≥ 0.3.50 and ≤ 0.9.7	Vulnerable	NIST National Vulnerability Database
F5	Nginx Plus	≥ R32 and < R32 P6≥ R36 and < R36 P4	Vulnerable	CVE Program (cve.org) e CISA ADP
F5	Nginx Plus	≥ r32 and ≤ r36	Vulnerable	NIST National Vulnerability Database
F5	Waf	≥ 4.9.0 and ≤ 4.16.0≥ 5.1.0 and ≤ 5.8.0≥ 5.9.0 and ≤ 5.12.1	Vulnerable	NIST National Vulnerability Database

Attack characteristics

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

Attack vector

Network

Attack complexity

High

Privileges required

None

User interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

Low

Every base score collected

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

Score	Version	Severity	Expl.	Impact	Scored by
6.3	CVSS 4.0	Medium	—	—	f5sirt@f5.com via NIST National Vulnerability Database
6.3	CVSS 4.0	Medium	—	—	f5 via CVE Program (cve.org) e CISA ADP
4.8	CVSS 3.1	Medium	2.2	2.5	f5sirt@f5.com via NIST National Vulnerability Database
4.8	CVSS 3.1	Medium	—	—	f5 via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L (score shown at the top: f5sirt@f5.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-125 · Out-of-bounds Read

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.73%

Detection

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

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.

web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

2026
Affected products added · f5/nginx plus, f5/nginx open source
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
CVSS changed · 4.8
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
May 13, 2026 · f5

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

1 on the record

my.f5.com/manage/s/article/K000161028
Mitigation, Vendor Advisory, vendor-advisory, patch, NIST National Vulnerability Database

Elsewhere on this site

F5
every CVE for this vendor

Memory corruption
same class

CWE-125
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-97205 NGINX ngx_http_core_module vulnerability 1d
Medium CVE-2026-96615 NGINX Gateway Fabric vulnerability 1d
Medium CVE-2026-97629 NGINX ngx_http_ssl_module vulnerability 1d
Medium CVE-2026-95101 NGINX ngx_http_v3_module vulnerability 1d
High CVE-2026-93479 NGINX map directive and regex matching vulnerability 1d
High CVE-2026-91184 NGINX Gateway Fabric vulnerability 1d

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 record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-42934 is "NGINX ngx_http_charset_module vulnerability", rated Medium. It affects Dos (F5); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 4.8 describes technical severity. EPSS 0.73% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.