CVE-2023-35943
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedEnvoy is an open source edge and service proxy designed for cloud-native applications. Prior to versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12, the CORS filter will segfault and crash Envoy when the `origin` header is removed and deleted between `decodeHeaders`and `encodeHeaders`. Versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12 have a fix for this issue. As a workaround, do not remove the `origin` header in the Envoy configuration.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisMemory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.
General guidance for the use after free class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 1.23.0, < 1.23.12>= 1.24.0, < 1.24.10>= 1.25.0, < 1.25.9>= 1.26.0, < 1.26.4CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped1.23.121.24.101.25.9
Upgrade to Envoy 1.23.12, 1.24.10, 1.25.9, 1.26.4, or 1.27.0 (or later) depending on current version branch
- 1. Identify the current Envoy version in use by checking the Envoy process or deployment configuration
- 2. Select the appropriate fixed version based on the current version branch: for 1.23.x upgrade to 1.23.12, for 1.24.x upgrade to 1.24.10, for 1.25.x upgrade to 1.25.9, for 1.26.x upgrade to 1.26.4
- 3. Obtain the Envoy binary or container image for the selected fixed version from the official Envoy release repository
- 4. Test the upgrade in a staging or non-production environment to verify the CORS filter no longer crashes when the origin header is manipulated
- 5. Deploy the upgraded Envoy version to production during a scheduled maintenance window
- 6. Verify that the CORS filter operates correctly and Envoy remains stable
Generated from the published advisory — verify against the referenced sources before acting.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-35943 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2023-35943 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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