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Limit length of base64 encoding buffers #2447

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c402339
tests: characterize extacl base64 stack buffer overflow
kinkie Jun 15, 2026
2125dc5
icap: fix extacl credential buffer overflow in makeRequestHeaders
kinkie Jun 17, 2026
3d1055f
http: fix extacl credential buffer overflows in httpFixupAuthentication
kinkie Jun 17, 2026
1c410dc
Merge remote-tracking branch 'upstream/master' into fix-base64encode
kinkie Jun 19, 2026
f6c053e
Apply aaa
kinkie Jun 20, 2026
ef95154
Remove test harness
kinkie Jun 20, 2026
d7fa149
Use TextException
kinkie Jun 20, 2026
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14 changes: 11 additions & 3 deletions src/adaptation/icap/ModXact.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1399,12 +1399,20 @@ void Adaptation::Icap::ModXact::makeRequestHeaders(MemBuf &buf)
String vh=virgin.header->header.getById(Http::HdrType::PROXY_AUTHORIZATION);
buf.appendf("Proxy-Authorization: " SQUIDSTRINGPH "\r\n", SQUIDSTRINGPRINT(vh));
} else if (request->extacl_user.size() > 0 && request->extacl_passwd.size() > 0) {
const auto userLen = request->extacl_user.size();
const auto passwdLen = request->extacl_passwd.size();
// +1 for the ':' separator between user and passwd
const auto plainLen = userLen + 1 + passwdLen;
if (plainLen > MAX_LOGIN_SZ)
throw TexcHere("extacl credentials too long for Proxy-Authorization");
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// plainLen <= MAX_LOGIN_SZ, so base64_encode_len(plainLen) fits
// within the base64_encode_len(MAX_LOGIN_SZ) stack buffer.
Comment on lines +1408 to +1409

@rousskov rousskov Jun 26, 2026

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I do not think we need to add this comment -- this code is quite self-documenting/clear.

Suggested change
// plainLen <= MAX_LOGIN_SZ, so base64_encode_len(plainLen) fits
// within the base64_encode_len(MAX_LOGIN_SZ) stack buffer.

I do not insist on this change.

char base64buf[base64_encode_len(MAX_LOGIN_SZ)];
Comment on lines +1406 to +1410

@yadij yadij Jun 22, 2026 •
edited
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Suggested change
if (plainLen > MAX_LOGIN_SZ)
throw TextException("extacl credentials too long for Proxy-Authorization", Here());
// plainLen <= MAX_LOGIN_SZ, so base64_encode_len(plainLen) fits
// within the base64_encode_len(MAX_LOGIN_SZ) stack buffer.
char base64buf[base64_encode_len(MAX_LOGIN_SZ)];
SBuf encoded; // TODO: when 'buf' is an SBuf we can write directly to it.
auto base64buf = encoded.rawAppendStart(base64_encode_len(plainLen));

@yadij yadij Jun 26, 2026

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If you want to be particularly pedantic, you can also verify that the final output will fit into the allocated MemBuf output parameter as well as within the temporary buffer allocation:

Suggested change
if (plainLen > MAX_LOGIN_SZ)
throw TextException("extacl credentials too long for Proxy-Authorization", Here());
// plainLen <= MAX_LOGIN_SZ, so base64_encode_len(plainLen) fits
// within the base64_encode_len(MAX_LOGIN_SZ) stack buffer.
char base64buf[base64_encode_len(MAX_LOGIN_SZ)];
const auto expectedSize = base64_encode_len(plainLen)
+ 28 /* HTTP Syntax: "Proxy-Authorization: Basic " */
+ 30 /* HTTP Syntax: CRLF */;
Assure(buf.potentialSpaceSize() > expectedSize);
SBuf encoded; // TODO: when 'buf' is an SBuf we can write directly to it.
auto base64buf = encoded.rawAppendStart(base64_encode_len(plainLen));

That TODO could technically be implemented today with buf.rawSpace(). Provided its space was resized first to ensure the buffer existed before being passed to the encoder. Currently it may not exist and appendf() after encoder does any needed allocation as a repeat allocation. My suggested SBuf use avoids that extra code being part of this patch.

struct base64_encode_ctx ctx;
base64_encode_init(&ctx);
char base64buf[base64_encode_len(MAX_LOGIN_SZ)];
size_t resultLen = base64_encode_update(&ctx, base64buf, request->extacl_user.size(), reinterpret_cast<const uint8_t*>(request->extacl_user.rawBuf()));
auto resultLen = base64_encode_update(&ctx, base64buf, userLen, reinterpret_cast<const uint8_t*>(request->extacl_user.rawBuf()));
resultLen += base64_encode_update(&ctx, base64buf+resultLen, 1, reinterpret_cast<const uint8_t*>(":"));
resultLen += base64_encode_update(&ctx, base64buf+resultLen, request->extacl_passwd.size(), reinterpret_cast<const uint8_t*>(request->extacl_passwd.rawBuf()));
resultLen += base64_encode_update(&ctx, base64buf+resultLen, passwdLen, reinterpret_cast<const uint8_t*>(request->extacl_passwd.rawBuf()));
resultLen += base64_encode_final(&ctx, base64buf+resultLen);
buf.appendf("Proxy-Authorization: Basic %.*s\r\n", (int)resultLen, base64buf);

@yadij yadij Jun 22, 2026

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Suggested change
buf.appendf("Proxy-Authorization: Basic %.*s\r\n", (int)resultLen, base64buf);
encoded.rawAppendFinish(base64buf, resultLen);
buf.appendf("Proxy-Authorization: Basic " SQUIDSBUFPH "\r\n", SQUIDSBUFPRINT(encoded));

}
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22 changes: 17 additions & 5 deletions src/http.cc
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Expand Up @@ -1850,8 +1850,12 @@ httpFixupAuthentication(HttpRequest * request, const HttpHeader * hdr_in, HttpHe
username = request->auth_user_request->username();
#endif

blen = base64_encode_update(&ctx, loginbuf, strlen(username), reinterpret_cast<const uint8_t*>(username));
blen += base64_encode_update(&ctx, loginbuf+blen, strlen(request->peer_login +1), reinterpret_cast<const uint8_t*>(request->peer_login +1));
const auto usernameLen = strlen(username);
const auto suffixLen = strlen(request->peer_login + 1);
if (usernameLen + suffixLen > MAX_LOGIN_SZ)
throw TexcHere("peer login credentials too long");
blen = base64_encode_update(&ctx, loginbuf, usernameLen, reinterpret_cast<const uint8_t*>(username));
blen += base64_encode_update(&ctx, loginbuf+blen, suffixLen, reinterpret_cast<const uint8_t*>(request->peer_login +1));
blen += base64_encode_final(&ctx, loginbuf+blen);
httpHeaderPutStrf(hdr_out, header, "Basic %.*s", (int)blen, loginbuf);
return;
Expand All @@ -1862,9 +1866,14 @@ httpFixupAuthentication(HttpRequest * request, const HttpHeader * hdr_in, HttpHe
(strcmp(request->peer_login, "PASS") == 0 ||
strcmp(request->peer_login, "PROXYPASS") == 0)) {

blen = base64_encode_update(&ctx, loginbuf, request->extacl_user.size(), reinterpret_cast<const uint8_t*>(request->extacl_user.rawBuf()));
const auto userLen = request->extacl_user.size();
const auto passwdLen = request->extacl_passwd.size();
// +1 for the ':' separator between user and passwd
if (userLen + 1 + passwdLen > MAX_LOGIN_SZ)
throw TexcHere("extacl credentials too long for peer login");
blen = base64_encode_update(&ctx, loginbuf, userLen, reinterpret_cast<const uint8_t*>(request->extacl_user.rawBuf()));
blen += base64_encode_update(&ctx, loginbuf+blen, 1, reinterpret_cast<const uint8_t*>(":"));
blen += base64_encode_update(&ctx, loginbuf+blen, request->extacl_passwd.size(), reinterpret_cast<const uint8_t*>(request->extacl_passwd.rawBuf()));
blen += base64_encode_update(&ctx, loginbuf+blen, passwdLen, reinterpret_cast<const uint8_t*>(request->extacl_passwd.rawBuf()));
blen += base64_encode_final(&ctx, loginbuf+blen);
httpHeaderPutStrf(hdr_out, header, "Basic %.*s", (int)blen, loginbuf);
return;
Expand Down Expand Up @@ -1894,7 +1903,10 @@ httpFixupAuthentication(HttpRequest * request, const HttpHeader * hdr_in, HttpHe
}
#endif /* HAVE_KRB5 && HAVE_GSSAPI */

blen = base64_encode_update(&ctx, loginbuf, strlen(request->peer_login), reinterpret_cast<const uint8_t*>(request->peer_login));
const auto loginLen = strlen(request->peer_login);
if (loginLen > MAX_LOGIN_SZ)
throw TexcHere("peer_login too long");
blen = base64_encode_update(&ctx, loginbuf, loginLen, reinterpret_cast<const uint8_t*>(request->peer_login));
blen += base64_encode_final(&ctx, loginbuf+blen);
httpHeaderPutStrf(hdr_out, header, "Basic %.*s", (int)blen, loginbuf);

@rousskov rousskov Jun 20, 2026 •
edited
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Please add Assure(request->url.userInfo().length() < MAX_URL*2) or a similar assertion to HttpStateData::httpBuildRequestHeader().

Please also adjust SSP_MakeChallenge() and peer_proxy_negotiate_auth() cases.

@yadij yadij Jun 26, 2026 •
edited
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Good spot, however those cases should be restricted by MAX_AUTHTOKEN_SZ which is the SSPI buffer size for encoded credential tokens.

So Assure(base64_encode_len(loginLen) <= MAX_AUTHTOKEN_LEN);

@rousskov rousskov Jun 26, 2026

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Good spot, however those cases should be restricted by MAX_AUTHTOKEN_SZ which is the SSPI buffer size for encoded credential tokens.

I do not recommend changing the size of the existing assembly buffer in this PR. The current size is MAX_URL*2, not MAX_AUTHTOKEN_SZ (which is presumably a typo for MAX_AUTHTOKEN_LEN).

If you do increase that size despite my recommendation, please update or remove the corresponding "should be big enough for a single URI segment" comment as well: MAX_AUTHTOKEN_LEN is much bigger than MAX_URL or even MAX_URL*2, so the comment would become even more wrong/misleading (and you become responsible for updating or removing it if you change the size).

return;
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