Process crash via bodyless 303 internal redirect
Published Jun 26, 2026 · Updated Jun 26, 2026
Null pointer dereference in the Envoy router filter allows remote attackers to crash the proxy through an HTTP 303 internal redirect. For a body-less POST, PUT, DELETE, or PATCH request, the router's 303 conversion path calls modifyDecodingBuffer on a buffer that decodeData never allocated. Exploitation requires an internal_redirect_policy that includes 303 and an upstream 303 response; the resulting SIGSEGV terminates Envoy and all active connections.
Summary
What happened
Null pointer dereference in the Envoy router filter allows remote attackers to crash the proxy through an HTTP 303 internal redirect. For a body-less POST, PUT, DELETE, or PATCH request, the router's 303 conversion path calls modifyDecodingBuffer on a buffer that decodeData never allocated. Exploitation requires an internal_redirect_policy that includes 303 and an upstream 303 response; the resulting SIGSEGV terminates Envoy and all active connections.
The record
- CVE
- CVE-2026-47221
- Published
- Jun 26, 2026
- Updated
- Jun 26, 2026
- Vendor
- Envoy Proxy
- Product
- Envoy
- Classifications
- CWE-476, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 26, 2026CVE publishedPublication date reported by the CVE source.
- Jun 26, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=>= 1.18.0, < 1.35.13
- Affected versionversion=>= 1.36.0, < 1.36.9
- Affected versionversion=>= 1.37.0, < 1.37.5
- Affected versionversion=>= 1.38.0, < 1.38.3
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Envoy bodyless 303 internal-redirect PoCproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
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