Summary
In the Linux kernel, the following vulnerability has been resolved: RDMA/siw: Fix the sendmsg...
In the Linux kernel, the following vulnerability has been resolved:
RDMA/siw: Fix the sendmsg byte count in siw_tcp_sendpages
Ever since commit c2ff29e99a76 ("siw: Inline do_tcp_sendpages()"),
we have been doing this:
static int siw_tcp_sendpages(struct socket *s, struct page *page, int offset,
size_t size)
[...]
/ Calculate the number of bytes we need to push, for this page
* specifically /
size_t bytes = min_t(size_t, PAGE_SIZE - offset, size);
/ If we can't splice it, then copy it in, as normal /
if (!sendpage_ok(page[i]))
msg.msg_flags &= ~MSG_SPLICE_PAGES;
/ Set the bvec pointing to the page, with len $bytes /
bvec_set_page(&bvec, page[i], bytes, offset);
/ Set the iter to $size, aka the size of the whole sendpages (!!!) /
iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
try_page_again:
lock_sock(sk);
/ Sendmsg with $size size (!!!) */
rv = tcp_sendmsg_locked(sk, &msg, size);
This means we've been sending oversized iov_iters and tcp_sendmsg calls
for a while. This has a been a benign bug because sendpage_ok() always
returned true. With the recent slab allocator changes being slowly
introduced into next (that disallow sendpage on large kmalloc
allocations), we have recently hit out-of-bounds crashes, due to slight
differences in iov_iter behavior between the MSG_SPLICE_PAGES and
"regular" copy paths:
(MSG_SPLICE_PAGES)
skb_splice_from_iter
iov_iter_extract_pages
iov_iter_extract_bvec_pages
uses i->nr_segs to correctly stop in its tracks before OoB'ing everywhere
skb_splice_from_iter gets a "short" read
(!MSG_SPLICE_PAGES)
skb_copy_to_page_nocache copy=iov_iter_count
[...]
copy_from_iter
/* this doesn't help */
if (unlikely(iter->count < len))
len = iter->count;
iterate_bvec
... and we run off the bvecs
Fix this by properly setting the iov_iter's byte count, plus sending the
correct byte count to tcp_sendmsg_locked.
Impact
CVE-2025-39758 has a CVSS score of 5.5 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2025-39758? CVE-2025-39758 is a medium-severity security vulnerability. No fixed version is listed yet.
- How severe is CVE-2025-39758? CVE-2025-39758 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Is there a fix for CVE-2025-39758? No fixed version is listed for CVE-2025-39758 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2025-39758 exploitable, and should I be worried? Whether CVE-2025-39758 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-39758 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.