CVE-2026-26309
CVE-2026-26309 is a medium-severity vulnerability in Envoyproxy Envoy with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-193.
Key facts
- Severity: Medium (CVSS 3.x base score 5.3)
- EPSS exploit prediction: 0% (29th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-10800
- Weakness: CWE-193
- Affected product: Envoyproxy Envoy
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-26309?
- 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.
- How severe is CVE-2026-26309?
- CVE-2026-26309 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
- Is CVE-2026-26309 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (29th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-26309?
- CVE-2026-26309 primarily affects Envoyproxy Envoy. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
- How do I fix CVE-2026-26309?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-26309 have an EU (EUVD) identifier?
- Yes. CVE-2026-26309 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-10800.
- When was CVE-2026-26309 published?
- CVE-2026-26309 was published on 2026-03-10 and last updated on 2026-06-17.
References
Affected products (2)
- cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*
- cpe:2.3:a:envoyproxy:envoy:1.37.0:*:*:*:*:*:*:*
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- CVE-2019-18801 — Critical (CVSS 9.8): An issue was discovered in Envoy 1.12.0. An untrusted remote client may send HTTP/2 requests that write to the heap…
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- CVE-2024-23324 — High (CVSS 8.6): Envoy is a high-performance edge/middle/service proxy. External authentication can be bypassed by downstream…
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