Prevent malformed upload path causing arbitrary write#1170
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marty1885 wants to merge 4 commits intodrogonframework:masterfrom
Closed
Prevent malformed upload path causing arbitrary write#1170marty1885 wants to merge 4 commits intodrogonframework:masterfrom
marty1885 wants to merge 4 commits intodrogonframework:masterfrom
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Kirill89
reviewed
Jan 30, 2022
| fsFileName = fsUploadPath / fsFileName; | ||
| } | ||
| fsFileName = fsFileName.lexically_normal(); | ||
| if (fsFileName.is_relative()) |
Contributor
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Unfortunately it is not enough to check if path is not relative. In this case if filename_ will be /malicious-file user still will be able to upload outside of uploads folder.
Can I suggest to do something like:
int HttpFileImpl::save(const std::string &path) const
{
assert(!path.empty());
if (fileName_.empty())
return -1;
filesystem::path fsPath(utils::toNativePath(path));
if (!fsPath.is_absolute() &&
(!fsPath.has_parent_path() ||
(fsPath.begin()->string() != "." && fsPath.begin()->string() != "..")))
{
filesystem::path fsUploadPath(utils::toNativePath(
HttpAppFrameworkImpl::instance().getUploadPath()));
fsPath = fsUploadPath / fsPath;
}
fsPath += "/";
fsPath = fsPath.lexically_normal();
auto fsSaveToPath = filesystem::path(fsPath);
fsSaveToPath += filesystem::path(utils::toNativePath(fileName_));
fsSaveToPath = fsSaveToPath.lexically_normal();
if (fsSaveToPath.string().find(fsPath.string(), 0) != 0)
{
LOG_ERROR
<< "Attempt writing outside of upload directory detected. Path: "
<< fileName;
return -1;
}
// ...
return saveTo(fsSaveToPath);
- You need to clean all multiple slashes and dot segments –
lexically_normal. - Concatenate path with
std::filesystem::path::concat(+= operator) instead ofstd::filesystem::path::append(/ operator) because if the second argument ofappendis an absolute path it will resolve the whole path to the second argument. - Call
lexically_normalagain to avoid//after concat. - And then you need to check if final upload path starts with the uploads folder path.
Alternatively you can drop all .. and / symbols from the fileName_.
Member
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@Kirill89 I am very grateful for your advice. we'll fix this.
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This PR prevents a malformed upload path causing the upload function to write outside of the destination directory by checking the upload path.
TBH I'm not 100% sure my patch fixes everything and didn't break unintentionally. Need some review.