VulnerabilityPublished 26 Jun 2026

CVE-2026-47778: envoyproxy envoy · Improper Neutralization of Null Byte or NUL Character

Affects envoyproxy envoySource CVE Database V5

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Not known to be exploited · CVSS 4.4 Medium · fixed in 1.38.1 : update envoyproxy envoy when convenient.

Data as of 7 Nov 2026, 23:24 UTC

CVSS 3.1 base score

4.4Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 11% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.38.1, 1.37.3, 1.36.7 +1

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: High
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: High: The attacker is authorized with (i.e., requires) privileges that provide significant (e.g., administrative) control over the vulnerable component that could affect component-wide settings and files.
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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within 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 26 Jun 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
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), the Metasploit, Exploit-DB and nuclei-templates index as of 7 Nov 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 envoy and envoyproxy/envoy to 1.38.1, 1.37.3, 1.36.7 or 1.35.11.

Affected software

Product	Affected	Fixed in
envoyproxyenvoy	Affected >=1.38.0 <1.38.1	Fixed in 1.38.1
envoyproxyenvoy	Affected >=1.37.0 <1.37.3	Fixed in 1.37.3
envoyproxyenvoy	Affected >=1.36.0 <1.36.7	Fixed in 1.36.7
envoyproxyenvoy	Affected <1.35.11	Fixed in 1.35.11
GitHubenvoyproxy/envoy`pkg:github/envoyproxy/envoy`Other threats	Affected <1.35.11 <1.36.7 <1.37.3 <1.38.1	Fixed in 1.35.11 1.36.7 1.37.3 1.38.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

This vulnerability is fixed in Envoy versions 1.35.11, 1.36.7, 1.37.3, and 1.38.1. Users should upgrade to one of these versions or later to remediate the issue. Patch status is confirmed by the version information provided. No additional vendor advisory content is available, so check the official Envoy release notes for confirmation and further guidance.

Description

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, a structural flaw was identified in DefaultCertValidator::verifySubjectAltName where the extracted DNS SAN string is cast to a C-style string using .c_str() before being passed to the Utility::dnsNameMatch() algorithm. If the attacker serves a certificate with a dNSName SAN containing an embedded NUL byte, the helper Utility::generalNameAsString captures the complete string including the NUL. However, when .c_str() evaluates it, implicit conversion to absl::string_view inside dnsNameMatch relies on strlen(), prematurely truncating the evaluation context. Envoy evaluates trucated string against the exact required config_san match and returns true, thereby successfully validating the string with the Nul byte for an upstream routing. This vulnerability is fixed in 1.35.11, 1.36.7, 1.37.3, and 1.38.1.

Impact

Successful exploitation allows an attacker to bypass DNS SAN validation in Envoy, potentially causing Envoy to accept and route traffic based on a certificate with a manipulated SAN field containing a null byte. This could lead to unauthorized upstream routing decisions. The CVSS score indicates a medium severity impact with high confidentiality impact but no integrity or availability impact. No known exploits in the wild have been reported.

Summary

Envoyproxy's envoy component has a vulnerability (CVE-2026-47778) involving improper neutralization of null bytes (CWE-158) in the certificate SAN validation process. Specifically, in versions prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, the DefaultCertValidator::verifySubjectAltName function casts the extracted DNS SAN string to a C-style string using .c_str() before passing it to the dnsNameMatch algorithm. Because .c_str() relies on strlen(), it truncates the string at the embedded null byte, allowing an attacker to craft a certificate with a dNSName SAN containing a null byte that bypasses exact SAN matching. This results in Envoy incorrectly validating the SAN and permitting upstream routing based on the manipulated certificate. The vulnerability has a CVSS 3.1 score of 4.4 (medium severity) and is fixed in the specified versions.

CWE-158Improper Neutralization of Null Byte or NUL Character (opens in a new tab)
Variant weakness
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes NUL characters or null bytes when they are sent to a downstream component.
Developers should anticipate that null characters or null bytes will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
Implementation · Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174).
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
Server Side Request Forgery Prevention (opens in a new tab)
Unvalidated Redirects and Forwards (opens in a new tab)
Cross Site Scripting Prevention (opens in a new tab)
OWASP ASVS 4.0.3
V1.5.1 (opens in a new tab)
V5.2.2 (opens in a new tab)
Attack patterns
Embedding NULL Bytes (opens in a new tab)
Postfix, Null Terminate, and Backslash (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/envoyproxy/envoy/security/advisories/GHSA-f8x4-rw5x-f3r7 (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 3 Jul 2026, 22:35 UTC

WeaknessesCWE-158

Technical details

References

Community reviews

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