Home » Chrome: DNS requests with random DNS names: malware?

Chrome: DNS requests with random DNS names: malware?

Solutons:


I found a series of posts/bug reports about random DNS requests made by Chrome. The conclusion is that random DNS requests are neither generated by malware nor by plugins or add-ons.

The requests are done by Chrome, to learn if it can handle searches made from its address bar.

The best explanation I have found is quoted below, from this link.

If you type in a single-word search query, chrome needs to send a DNS
request to check if this might be a single-word host name: For
example, “test” might be a search for “test” or a navigation to
“http://test”. If the query ends up being a host, chrome shows an
infobar that asks “did you mean to go to ‘test’ instead”. For performance
reasons, the DNS query needs to be asynchronous.

Now some ISPs started showing ads for non-existent domain names (
http://en.wikipedia.org/wiki/DNS_hijacking ), meaning Chrome would
always show that infobar for every single-word query. Since this is
annoying, chrome now sends three random DNS requests at startup, and
if they all resolve (to the same IP, I think), it now knows not to
show the “did you mean” infobar for single-word queries that resolve
to that IP.

Beyond ISP level or malware DNS hijacking, mentioned in the Wikipedia entry above, some paid wireless access points or captive portals also hijack DNS. Random requests are made at seemingly random intervals,and not just when starting Chrome. At least, they happen each time the current network interface gets a new IP address.

Here is another link related to the theme from @Gilles: Unusual HEAD requests to nonsense URLs from Chrome. Hence, adding to the question the topic of proxy test setup. You end up seeing proxy logs because, when a proxy is configured, the requests are made via the proxy; and, it is up to the proxy to resolve the DNS requests.

Lacking more solid details online, I downloaded and perused the Chromium source code, with the command below.

git clone https://chromium.googlesource.com/chromium/src 

The quote below was copied from the Chromium source code comments:

Because this function can be called during startup, when kicking off a
URL fetch can eat up 20 ms of time, we delay seven seconds, which is
hopefully long enough to be after startup, but still get results back
quickly.

This component sends requests to three randomly generated, and thus likely
nonexistent, hostnames. If at least two redirect to the same
hostname, this suggests the ISP is hijacking NXDOMAIN, and the omnibox
should treat similar redirected navigations as ‘failed’ when deciding
whether to prompt the user with a ‘did you mean to navigate’ infobar
for certain search inputs.

trigger: “On startup and when IP address of the computer changes.”

We generate a random hostname with between 7 and 15 characters.

My conclusion is that those random DNS request names are not a manifestation of malware behaviour ; they are probes for Chromium (and Google Chrome) to learn what it can do, concerning at least searches.

Lacking more solid details online, I downloaded the Chromium sources in my investigation. The logic dealing with this functionality can be found at in the file, src/chrome/browser/intranet_redirect_detector.cc and src/chrome/browser/ui/omnibox/chrome_omnibox_navigation_observer.cc.

Below is an excerpt of src/chrome/browser/intranet_redirect_detector.cc:

void IntranetRedirectDetector::FinishSleep() {
  in_sleep_ = false;

  // If another fetch operation is still running, cancel it.
  fetchers_.clear();
  resulting_origins_.clear();

  const base::CommandLine* cmd_line = base::CommandLine::ForCurrentProcess();
  if (cmd_line->HasSwitch(switches::kDisableBackgroundNetworking))
    return;

  DCHECK(fetchers_.empty() && resulting_origins_.empty());

  // Create traffic annotation tag.
  net::NetworkTrafficAnnotationTag traffic_annotation =
      net::DefineNetworkTrafficAnnotation("intranet_redirect_detector", R"(
        semantics {
          sender: "Intranet Redirect Detector"
          description:
            "This component sends requests to three randomly generated, and "
            "thus likely nonexistent, hostnames.  If at least two redirect to "
            "the same hostname, this suggests the ISP is hijacking NXDOMAIN, "
            "and the omnibox should treat similar redirected navigations as "
            "'failed' when deciding whether to prompt the user with a 'did you "
            "mean to navigate' infobar for certain search inputs."
          trigger: "On startup and when IP address of the computer changes."
          data: "None, this is just an empty request."
          destination: OTHER
        }
        policy {
          cookies_allowed: false
          setting: "This feature cannot be disabled by settings."
          policy_exception_justification:
              "Not implemented, considered not useful."
        })");

  // Start three fetchers on random hostnames.
  for (size_t i = 0; i < 3; ++i) {
    std::string url_string("http://");
    // We generate a random hostname with between 7 and 15 characters.
    const int num_chars = base::RandInt(7, 15);
    for (int j = 0; j < num_chars; ++j)
      url_string += ('a' + base::RandInt(0, 'z' - 'a'));
    GURL random_url(url_string + "https://unix.stackexchange.com/");
    std::unique_ptr<net::URLFetcher> fetcher = net::URLFetcher::Create(
        random_url, net::URLFetcher::HEAD, this, traffic_annotation);
    // We don't want these fetches to affect existing state in the profile.
    fetcher->SetLoadFlags(net::LOAD_DISABLE_CACHE |
                          net::LOAD_DO_NOT_SAVE_COOKIES |
                          net::LOAD_DO_NOT_SEND_COOKIES |
                          net::LOAD_DO_NOT_SEND_AUTH_DATA);
    fetcher->SetRequestContext(g_browser_process->system_request_context());
    fetcher->Start();
    net::URLFetcher* fetcher_ptr = fetcher.get();
    fetchers_[fetcher_ptr] = std::move(fetcher);
  }
}

void IntranetRedirectDetector::OnURLFetchComplete(
    const net::URLFetcher* source) {
  // Delete the fetcher on this function's exit.
  auto it = fetchers_.find(const_cast<net::URLFetcher*>(source));
  DCHECK(it != fetchers_.end());
  std::unique_ptr<net::URLFetcher> fetcher = std::move(it->second);
  fetchers_.erase(it);

  // If any two fetches result in the same domain/host, we set the redirect
  // origin to that; otherwise we set it to nothing.
  if (!source->GetStatus().is_success() || (source->GetResponseCode() != 200)) {
    if ((resulting_origins_.empty()) ||
        ((resulting_origins_.size() == 1) &&
         resulting_origins_.front().is_valid())) {
      resulting_origins_.push_back(GURL());
      return;
    }
    redirect_origin_ = GURL();
  } 

….

Below is an excerpt of the file, src/chrome/browser/ui/omnibox/chrome_omnibox_navigation_observer.cc:

// Returns true if |final_url| doesn't represent an ISP hijack of
// |original_url|, based on the IntranetRedirectDetector's RedirectOrigin().
bool IsValidNavigation(const GURL& original_url, const GURL& final_url) {

….

void ChromeOmniboxNavigationObserver::NavigationEntryCommitted(
    const content::LoadCommittedDetails& load_details) {
  load_state_ = LOAD_COMMITTED;
  if (ResponseCodeIndicatesSuccess(load_details.http_status_code) &&
      IsValidNavigation(match_.destination_url,
                        load_details.entry->GetVirtualURL()))
    OnSuccessfulNavigation();
  if (!fetcher_ || (fetch_state_ != FETCH_NOT_COMPLETE))
    OnAllLoadingFinished();  // deletes |this|!
}

void ChromeOmniboxNavigationObserver::OnURLFetchComplete(
    const net::URLFetcher* source) {
  DCHECK_EQ(fetcher_.get(), source);
  const net::URLRequestStatus& status = source->GetStatus();
  int response_code = source->GetResponseCode();
  fetch_state_ =
      (status.is_success() && ResponseCodeIndicatesSuccess(response_code)) ||
              ((status.status() == net::URLRequestStatus::CANCELED) &&
               ((response_code / 100) == 3) &&
               IsValidNavigation(alternate_nav_match_.destination_url,
                                 source->GetURL()))
          ? FETCH_SUCCEEDED
          : FETCH_FAILED;
  if (load_state_ == LOAD_COMMITTED)
    OnAllLoadingFinished();  // deletes |this|!
}

Related link: Mixed case DNS requests – Malware in my network?.

Slightly related: Why does Chromium not cache DNS for more than a minute?

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