CVE-2026-5244
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 · uneditedA vulnerability has been found in Cesanta Mongoose up to 7.20. This affects the function mg_tls_recv_cert of the file mongoose.c of the component TLS 1.3 Handler. Such manipulation of the argument pubkey leads to heap-based buffer overflow. The attack may be launched remotely. The exploit has been disclosed to the public and may be used. Upgrading to version 7.21 mitigates this issue. The name of the patch is 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. It is advisable to upgrade the affected component. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product.
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 analysis · high confidenceHeap-based buffer overflow vulnerability in Cesanta Mongoose web server library's TLS 1.3 handler component. The overflow occurs in the mg_tls_recv_cert function when processing the pubkey argument, allowing remote attackers to potentially execute arbitrary code or cause denial of service.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
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>= 7.0, < 7.21CVSS 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
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify the installed Cesanta Mongoose versionLocate the mongoose library in your project (check source files, header files like mongoose.h, or linked binary). Look for version definitions in the source code, such as MG_VERSION macro, or check the library filename which may contain the version string.Affected if The version is 7.0 through 7.20 inclusive, or if the version cannot be determined but the library code contains the vulnerable mg_tls_recv_cert function from the affected versions.
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Confirm TLS 1.3 support is enabledReview your Mongoose configuration and initialization code. Look for TLS-related flags or options such as MG_TLS_FLAG_TLS_13, or examine build configuration files for TLS 1.3 being compiled in. Check if your application initializes TLS connections using MG_TLS or mg_tls_ctx.Affected if TLS 1.3 support is enabled in the build or configuration.
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Verify the mg_tls_recv_cert function is presentSearch the mongoose source code or binary for the function mg_tls_recv_cert. In source code, this can be done with grep or similar tools. In compiled binaries, use nm, objdump, or strings to locate this symbol.Affected if The function exists in the library, indicating the vulnerable TLS certificate handling code is present.
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Check for TLS certificate handling in your applicationReview application code that handles TLS certificate verification or reception. Look for calls that process certificates from remote peers in TLS 1.3 connections, particularly where the pubkey argument is passed to certificate processing functions.Affected if Your application processes TLS certificates from remote peers using Mongoose's TLS 1.3 implementation.
You are affected if you are using Cesanta Mongoose versions 7.0 through 7.20 with TLS 1.3 enabled and your application processes TLS certificates, as the heap buffer overflow in mg_tls_recv_cert can be triggered by malicious certificate data from a remote peer.
Generated from the published advisory. Verify against your own configuration.
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 · scoped7.21
Upgrade to Cesanta Mongoose version 7.21 or later to apply the patch (commit 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1). Given the critical CVSS 9.8 rating and public exploit availability, prioritize this upgrade immediately.
7.21
- Check the current Mongoose version in use (e.g., via package.json, requirements, or library inspection)
- Verify the version is >= 7.0 and < 7.21, confirming the system is vulnerable
- Update the Mongoose dependency to version 7.21 (e.g., npm update mongoose, pip install mongoose==7.21, or equivalent for your package manager)
- Rebuild or recompile any static bindings if applicable
- Verify the upgraded version is 7.21 by checking the library version
- Test the TLS functionality to confirm the fix does not introduce regressions
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-5244 — 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-2026-5244 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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- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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