VulnerabilityPublished 10 Mar 2026

CVE-2026-26309: envoyproxy envoy · Off-by-one Error

Affects envoyproxy envoySource CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium · fixed in 1.37.1 : update envoyproxy envoy when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

5.3Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 32% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.37.1, 1.36.5, 1.35.9 +1

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

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: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
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: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 10 Mar 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 30 Oct 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 to 1.37.1, 1.36.5, 1.35.9 or 1.34.13; envoyproxy/envoy to 1.34.13.

Affected software

Product	Affected	Fixed in
envoyproxyenvoy	Affected >=1.37.0 <1.37.1	Fixed in 1.37.1
envoyproxyenvoy	Affected >=1.36.0 <1.36.5	Fixed in 1.36.5
envoyproxyenvoy	Affected >=1.35.0 <1.35.9	Fixed in 1.35.9
envoyproxyenvoy	Affected <1.34.13	Fixed in 1.34.13
GitHubenvoyproxy/envoy`pkg:github/envoyproxy/envoy`Other threats	Affected <1.34.13	Fixed in 1.34.13

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

AI-suggested

To mitigate CVE-2026-26309, organizations should promptly upgrade Envoy to the fixed versions 1.37.1, 1.36.5, 1.35.8, or 1.34.13 depending on their current deployment version. In addition to patching, it is advisable to implement robust input validation and monitoring for abnormal proxy crashes or error patterns that could indicate exploitation attempts. Employing runtime protections such as memory safety tools (e.g., AddressSanitizer) during testing can help detect similar off-by-one errors early. Network-level protections like rate limiting and filtering suspicious traffic can reduce exposure to malformed JSON payloads. For environments using Envoy as part of a service mesh, ensure that control plane components are also updated to avoid cascading failures. Regularly review and audit proxy configurations and logs to detect anomalies. Finally, maintain an incident response plan that includes steps for rapid patch deployment and service restoration in case of a denial-of-service event.

Description

Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, an off-by-one write in Envoy::JsonEscaper::escapeString() can corrupt std::string null-termination, causing undefined behavior and potentially leading to crashes or out-of-bounds reads when the resulting string is later treated as a C-string. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.

Impact

The primary impact of CVE-2026-26309 is on the availability of services relying on vulnerable Envoy proxy versions. The off-by-one error can cause Envoy to crash or behave unpredictably when processing certain JSON strings, potentially leading to denial-of-service conditions. While confidentiality and integrity are not directly affected, service disruption can degrade user experience and impact dependent applications. Organizations using Envoy in critical infrastructure, cloud platforms, or service mesh deployments may face outages or instability if exploited. The vulnerability requires no authentication or user interaction, increasing the risk of remote exploitation. Although no active exploits are known, the widespread use of Envoy in modern cloud-native environments means that many organizations worldwide could be affected if attackers develop exploits. The impact is particularly significant for high-availability environments where proxy stability is essential for service continuity.

CWE-193Off-by-one Error (opens in a new tab)
Base weakness
A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.
Implementation
When copying character arrays or using character manipulation methods, the correct size parameter must be used to account for the null terminator that needs to be added at the end of the array.
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/envoyproxy/envoy/security/advisories/GHSA-56cj-wgg3-x943 (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Mar 2026, 19:45 UTC

WeaknessesCWE-193

Technical details

References

Community reviews

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