1503: Document retroactive attack risks and limitations

Author: ArneBab

content/2025-07-06-build-1503.md

@@ -1,7 +1,7 @@
 ---
 author: Arne Babenhauserheide
 layout: content
-title:  Freenet / Hyphanet build 1503: fix vulnerability and visibility, add animated webp, convenience, and optimization
+title:  Freenet / Hyphanet build 1502/1503: fix vulnerability and visibility, add animated webp, convenience, and optimization
 date:   2025-02-22
 categories: release
 ---
@@ -15,33 +15,59 @@ is a hotfix release that fixes regressions in 1502. The main changes are:
 
 <div style="float: right; width: 30%; max-width: 300px;"><img src="./theme/images/logo-large.png" width="100%" style="filter: invert(30%)"  /></div>
 
-- fixed vulnerability and reduce visibility on the network
+- fixed vulnerability
+- reduce visibility on the network
 - support animated webp and more modern HTML and CSS
-- enable direct linking to Freemail
+- enable direct linking to Freemail’s “New Message” page
 - dismiss alerts and convenience
 - substantial routing optimizations
 - fixes
 
-## vulnerability and visibility
+## mitigated vulnerability
 
 The most important change is a fix to a vulnerability that enabled
 attackers to differentiate between an uploading and a forwarding node
-by analyzing the structure of packets in blocks. It was reported
-responsibly by *Yonghuan Xu* and depended on block-level timing of
-packet handling.
+by analyzing the structure of packets in blocks. 
 
-Thank you very much for reporting the vulnerability and creating and
-testing a mitigation!
+The vulnerability enabled two attacks: one active and one passive.
+The active one could be exploited by depending on precise block-level
+timing of packet handling, forcing the node to expose if it was the
+original uploader of a file. The passive one worked by analyzing the
+packet structure inside blocks.
+
+While the active attack is completely mitigated, the passive attack
+could be done retroactively if an attacker had already recorded the
+full transmitted data on sub-block level.
+
+The attack has two limitations: it requires matching individual CHKs
+to keys, for example by downloading the key of the file at least once;
+this risk is highest for CHKs of known files and for
+re-uploads. And it requires a direct connection: it does not work
+against pure friend-to-friend mode when your friends are trustworthy.
+
+This vulnerability was reported responsibly by *Xu Yonghuan*. Thank
+you very much for the report and for creating and testing a
+mitigation!
+
+### fix regression: thread leak
 
 1503 fixed a thread leak from our adaption of the vulnerability
-mitigation that caused very fast nodes to restart within a few days,
-because the number of waiting threads exceeded the thread limit.
-Thanks to bertm for finding a minimally invasive solution and max_iops
-for reporting the problem and testing fixes!
+mitigation that caused very fast nodes to overload and slow down after
+a few days, because the number of waiting threads exceeded the thread
+limit. Don’t wait for zero, for it is infinite.
+
+Thanks to bertm for finding a minimally invasive solution and
+max_iops for reporting the problem and testing fixes!
+
+## visibility reduction and interface fixes
 
 There were some additional privacy and safety improvements: do not
 check reachability of global addresses to avoid a fallback to Echo
-packets when a node does not support Ping, don’t show download to disk
+packets when a node does not support Ping. These packets were a
+regression from 1498 due to a fallback in the platform address 
+checking when Ping is disabled.
+
+And don’t show download to disk
 for large file page on public gateway nodes, and make fproxy cross
 origin isolated -- the latter by torusrxxx.
 
@@ -63,8 +89,8 @@ visited again. Thanks to torusrxxx!
 
 ## link to freemail
 
-Also Freemail now allows inbound links with to=WOT_ID, so you can use  
-links on Freesites that directly open in Freemail.
+Freemail now allows inbound links to “/Freemail/NewMessage?to=\<WoT ID>”,
+so you can use links on Freesites that directly open in Freemail.
 
 ## dismiss alerts and convenience
 
@@ -82,7 +108,7 @@ nodes with many peers and make it easier to run simple routing nodes
 (without messaging) on weak, cheap, energy conserving hardware:
 
 - Fix synchronization of receive buffer -- #1044 by ArneBab. Thanks to
-  Yonguan Xu for the catch!
+  Xu Yonghuan for the catch!
 - Do not synchronize on global variable in CryptoKey.fingerprint --
   #1066 by bertm
 - Do not synchronize on access to AEADCryptBucket.readOnly -- #1065 by
@@ -124,7 +150,7 @@ And internal code fixes:
 - Fix single-byte read() in various InputStream implementations --
   #1058 by bertm
 
-And improvements to  the code to ease maintenance:
+And improvements to the code to ease maintenance:
 
 - 🐛 Allow Class Loader to Enumerate Directory Entries. Fixes Flyway
   usage -- #1049 by Bombe