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.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fix or patch referenced
- Who is exposed
- Default setups
Do first: Check every install: default setups are affected.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 31/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Default setups
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
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.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure22/25Default setups, reachable over the network without a login
- Reach?/20Unknown. No tracked technology or package matched
- Severity9.1/10CVSS 9.1
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
What to do
Check every install: default setups are affected.
Apply the patch listed under Evidence.
Workaround: For private CAs, use a verify CA file path (verify: '/path/ca.pem') with http.fetch or Request, or set SSL_CERT_FILE
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
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.
Timeline
- CVE published
- Record last updated
- First seen by cve.now
- Posted on X by cve.now
Affected versions
- vlang v
through 0.5.2
Evidence 5
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-82509
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: cve.now feed data
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: vulncheck.com, github.com
Which versions are affected by CVE-2026-82509?
v: through 0.5.2.Source: cve.now feed data
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: vulncheck.com, github.com
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: vulncheck.com, github.com