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<a href="https://gitlab.com/grey3228">Mikhail</a> created an issue: <a href="https://gitlab.com/gnutls/gnutls/-/issues/1777">#1777</a>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Hello!</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">I used SAST tool Svace to analyze gnutls <strong style="font-weight: 600; margin-top: 0;">3.8.11</strong> and encountered a possible buffer overflow in function <code style='font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>_srp_crypt</code>. In particular, the static buffer <code style='font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>result</code> in _srp_crypt() is only 1024 bytes, while the 8192-bit SRP group code produces base64-encoded verifier of 1366 characters.</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">I've checked it manually by creating tpasswd.conf file and then tried to create verifier with 8192-bit SRP group by specifying <code style='font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>--index=7</code>:</p>
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<pre class="code highlight js-syntax-highlight language-plaintext" v-pre="true" style='display: block; font-size: 14px; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; margin: 0 0 1rem; padding: 12px; border: 1px solid #dcdcde;'><code style='font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; background-color: inherit; border-radius: .25rem; white-space: pre; margin-top: 0; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;'><span id="LC1" class="line" lang="plaintext" style="margin-top: 0;">~$ srptool --passwd-conf ~/tpasswd.conf --passwd ~/tpasswd --username testuser --index=7</span></code></pre>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">gdb showed this:</p>
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<pre class="code highlight js-syntax-highlight language-plaintext" v-pre="true" style='display: block; font-size: 14px; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; margin: 0 0 1rem; padding: 12px; border: 1px solid #dcdcde;'><code style='font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; background-color: inherit; border-radius: .25rem; white-space: pre; margin-top: 0; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;'><span id="LC1" class="line" lang="plaintext" style="margin-top: 0;">(gdb) break srptool.c:468</span>
<span id="LC2" class="line" lang="plaintext">Breakpoint 1 at 0x2dce: file srptool.c, line 468.</span>
<span id="LC3" class="line" lang="plaintext">(gdb) run --passwd-conf ~/tpasswd.conf --passwd ~/tpasswd --username testuser --index=7</span>
<span id="LC4" class="line" lang="plaintext">Starting program: /usr/local/bin/srptool --passwd-conf ~/tpasswd.conf --passwd ~/tpasswd --username testuser --index=7</span>
<span id="LC5" class="line" lang="plaintext"></span>
<span id="LC6" class="line" lang="plaintext"><...></span>
<span id="LC7" class="line" lang="plaintext"></span>
<span id="LC8" class="line" lang="plaintext">Enter password: </span>
<span id="LC9" class="line" lang="plaintext"></span>
<span id="LC10" class="line" lang="plaintext">Breakpoint 1, _srp_crypt (username=0x7fffffffe21e "testuser", </span>
<span id="LC11" class="line" lang="plaintext"> passwd=0x55555557f130 "admin", salt_size=16, g=0x7fffffffb050, </span>
<span id="LC12" class="line" lang="plaintext"> n=0x7fffffffb040) at srptool.c:468</span>
<span id="LC13" class="line" lang="plaintext">468 sprintf(result, "%s:%s", txt_verifier.data, txt_salt.data);</span>
<span id="LC14" class="line" lang="plaintext">(gdb) print result</span>
<span id="LC15" class="line" lang="plaintext">$1 = '\000' <repeats 113 times></span>
<span id="LC16" class="line" lang="plaintext">(gdb) print txt_verifier.size</span>
<span id="LC17" class="line" lang="plaintext">$2 = 1366</span>
<span id="LC18" class="line" lang="plaintext">(gdb)</span></code></pre>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">However, program doesn't crash in this case in my env. But I've noticed, that I cannot then verify such password:</p>
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<pre class="code highlight js-syntax-highlight language-plaintext" v-pre="true" style='display: block; font-size: 14px; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; margin: 0 0 1rem; padding: 12px; border: 1px solid #dcdcde;'><code style='font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; background-color: inherit; border-radius: .25rem; white-space: pre; margin-top: 0; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;'><span id="LC1" class="line" lang="plaintext" style="margin-top: 0;">~$ srptool --verify --passwd-conf ~/tpasswd.conf --passwd ~/tpasswd --username testuser</span>
<span id="LC2" class="line" lang="plaintext">Enter password: </span>
<span id="LC3" class="line" lang="plaintext">Encoding error</span></code></pre>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">At the current moment I didn't find precise cause of such behavior because I'm newbie to gnutls srptool source code but I think it may be connected with out-of-bounds write, explained above..</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">At least, for addressing buffer overflow we could, f.e:</p>
<ul dir="auto" style="text-align: initial; list-style-type: disc; margin: 0 0 1rem; padding: 0;">
<li style="margin-top: 0; line-height: 1.6em; margin-left: 25px; padding-left: 3px;">increase the static buffer size to 2048 bytes (sufficient for all
currently supported groups),</li>
<li style="line-height: 1.6em; margin-left: 25px; padding-left: 3px;">replace sprintf() with snprintf() to prevent overflow even if the
buffer were accidentally too small.</li>
</ul>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">But unfortunately it doesn't help with <code style='font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>Encoding error</code> -- error remains. I wanted to open MR at first but for now I don't know how to deal with <code style='font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;'>Encoding error</code>, so fix would be incomplete or even wrong. Probably, I may misunderstand something important here, so sorry if I'm mistaking.</p>
<p dir="auto" style="color: #3a383f; margin: 0;" align="initial">Thank you upfront for your time and expertise!</p>
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