Linux: >> Linux Kernel >> 2.6.34.5 Security Vulnerabilities
In the Linux kernel, the following vulnerability has been resolved:
ipv6: avoid overflows in ip6_datagram_send_ctl()
Yiming Qian reported :
<quote>
I believe I found a locally triggerable kernel bug in the IPv6 sendmsg
ancillary-data path that can panic the kernel via `skb_under_panic()`
(local DoS).
The core issue is a mismatch between:
- a 16-bit length accumulator (`struct ipv6_txoptions::opt_flen`, type
`__u16`) and
- a pointer to the *last* provided destination-options header (`opt->dst1opt`)
when multiple `IPV6_DSTOPTS` control messages (cmsgs) are provided.
- `include/net/ipv6.h`:
- `struct ipv6_txoptions::opt_flen` is `__u16` (wrap possible).
(lines 291-307, especially 298)
- `net/ipv6/datagram.c:ip6_datagram_send_ctl()`:
- Accepts repeated `IPV6_DSTOPTS` and accumulates into `opt_flen`
without rejecting duplicates. (lines 909-933)
- `net/ipv6/ip6_output.c:__ip6_append_data()`:
- Uses `opt->opt_flen + opt->opt_nflen` to compute header
sizes/headroom decisions. (lines 1448-1466, especially 1463-1465)
- `net/ipv6/ip6_output.c:__ip6_make_skb()`:
- Calls `ipv6_push_frag_opts()` if `opt->opt_flen` is non-zero.
(lines 1930-1934)
- `net/ipv6/exthdrs.c:ipv6_push_frag_opts()` / `ipv6_push_exthdr()`:
- Push size comes from `ipv6_optlen(opt->dst1opt)` (based on the
pointed-to header). (lines 1179-1185 and 1206-1211)
1. `opt_flen` is a 16-bit accumulator:
- `include/net/ipv6.h:298` defines `__u16 opt_flen; /* after fragment hdr */`.
2. `ip6_datagram_send_ctl()` accepts *repeated* `IPV6_DSTOPTS` cmsgs
and increments `opt_flen` each time:
- In `net/ipv6/datagram.c:909-933`, for `IPV6_DSTOPTS`:
- It computes `len = ((hdr->hdrlen + 1) << 3);`
- It checks `CAP_NET_RAW` using `ns_capable(net->user_ns,
CAP_NET_RAW)`. (line 922)
- Then it does:
- `opt->opt_flen += len;` (line 927)
- `opt->dst1opt = hdr;` (line 928)
There is no duplicate rejection here (unlike the legacy
`IPV6_2292DSTOPTS` path which rejects duplicates at
`net/ipv6/datagram.c:901-904`).
If enough large `IPV6_DSTOPTS` cmsgs are provided, `opt_flen` wraps
while `dst1opt` still points to a large (2048-byte)
destination-options header.
In the attached PoC (`poc.c`):
- 32 cmsgs with `hdrlen=255` => `len = (255+1)*8 = 2048`
- 1 cmsg with `hdrlen=0` => `len = 8`
- Total increment: `32*2048 + 8 = 65544`, so `(__u16)opt_flen == 8`
- The last cmsg is 2048 bytes, so `dst1opt` points to a 2048-byte header.
3. The transmit path sizes headers using the wrapped `opt_flen`:
- In `net/ipv6/ip6_output.c:1463-1465`:
- `headersize = sizeof(struct ipv6hdr) + (opt ? opt->opt_flen +
opt->opt_nflen : 0) + ...;`
With wrapped `opt_flen`, `headersize`/headroom decisions underestimate
what will be pushed later.
4. When building the final skb, the actual push length comes from
`dst1opt` and is not limited by wrapped `opt_flen`:
- In `net/ipv6/ip6_output.c:1930-1934`:
- `if (opt->opt_flen) proto = ipv6_push_frag_opts(skb, opt, proto);`
- In `net/ipv6/exthdrs.c:1206-1211`, `ipv6_push_frag_opts()` pushes
`dst1opt` via `ipv6_push_exthdr()`.
- In `net/ipv6/exthdrs.c:1179-1184`, `ipv6_push_exthdr()` does:
- `skb_push(skb, ipv6_optlen(opt));`
- `memcpy(h, opt, ipv6_optlen(opt));`
With insufficient headroom, `skb_push()` underflows and triggers
`skb_under_panic()` -> `BUG()`:
- `net/core/skbuff.c:2669-2675` (`skb_push()` calls `skb_under_panic()`)
- `net/core/skbuff.c:207-214` (`skb_panic()` ends in `BUG()`)
- The `IPV6_DSTOPTS` cmsg path requires `CAP_NET_RAW` in the target
netns user namespace (`ns_capable(net->user_ns, CAP_NET_RAW)`).
- Root (or any task with `CAP_NET_RAW`) can trigger this without user
namespaces.
- An unprivileged `uid=1000` user can trigger this if unprivileged
user namespaces are enabled and it can create a userns+netns to obtain
namespaced `CAP_NET_RAW` (the attached PoC does this).
- Local denial of service: kernel BUG/panic (system crash).
-
---truncated---
CVSS Score
5.5
EPSS Score
0.0
Published
2026-04-13
In the Linux kernel, the following vulnerability has been resolved:
net: atm: fix crash due to unvalidated vcc pointer in sigd_send()
Reproducer available at [1].
The ATM send path (sendmsg -> vcc_sendmsg -> sigd_send) reads the vcc
pointer from msg->vcc and uses it directly without any validation. This
pointer comes from userspace via sendmsg() and can be arbitrarily forged:
int fd = socket(AF_ATMSVC, SOCK_DGRAM, 0);
ioctl(fd, ATMSIGD_CTRL); // become ATM signaling daemon
struct msghdr msg = { .msg_iov = &iov, ... };
*(unsigned long *)(buf + 4) = 0xdeadbeef; // fake vcc pointer
sendmsg(fd, &msg, 0); // kernel dereferences 0xdeadbeef
In normal operation, the kernel sends the vcc pointer to the signaling
daemon via sigd_enq() when processing operations like connect(), bind(),
or listen(). The daemon is expected to return the same pointer when
responding. However, a malicious daemon can send arbitrary pointer values.
Fix this by introducing find_get_vcc() which validates the pointer by
searching through vcc_hash (similar to how sigd_close() iterates over
all VCCs), and acquires a reference via sock_hold() if found.
Since struct atm_vcc embeds struct sock as its first member, they share
the same lifetime. Therefore using sock_hold/sock_put is sufficient to
keep the vcc alive while it is being used.
Note that there may be a race with sigd_close() which could mark the vcc
with various flags (e.g., ATM_VF_RELEASED) after find_get_vcc() returns.
However, sock_hold() guarantees the memory remains valid, so this race
only affects the logical state, not memory safety.
[1]: https://gist.github.com/mrpre/1ba5949c45529c511152e2f4c755b0f3
CVSS Score
5.5
EPSS Score
0.0
Published
2026-04-08
In the Linux kernel, the following vulnerability has been resolved:
media: dvb-net: fix OOB access in ULE extension header tables
The ule_mandatory_ext_handlers[] and ule_optional_ext_handlers[] tables
in handle_one_ule_extension() are declared with 255 elements (valid
indices 0-254), but the index htype is derived from network-controlled
data as (ule_sndu_type & 0x00FF), giving a range of 0-255. When
htype equals 255, an out-of-bounds read occurs on the function pointer
table, and the OOB value may be called as a function pointer.
Add a bounds check on htype against the array size before either table
is accessed. Out-of-range values now cause the SNDU to be discarded.
CVSS Score
9.8
EPSS Score
0.001
Published
2026-04-06
In the Linux kernel, the following vulnerability has been resolved:
netfilter: conntrack: add missing netlink policy validations
Hyunwoo Kim reports out-of-bounds access in sctp and ctnetlink.
These attributes are used by the kernel without any validation.
Extend the netlink policies accordingly.
Quoting the reporter:
nlattr_to_sctp() assigns the user-supplied CTA_PROTOINFO_SCTP_STATE
value directly to ct->proto.sctp.state without checking that it is
within the valid range. [..]
and: ... with exp->dir = 100, the access at
ct->master->tuplehash[100] reads 5600 bytes past the start of a
320-byte nf_conn object, causing a slab-out-of-bounds read confirmed by
UBSAN.
CVSS Score
7.1
EPSS Score
0.0
Published
2026-04-06
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: SCO: Fix use-after-free in sco_recv_frame() due to missing sock_hold
sco_recv_frame() reads conn->sk under sco_conn_lock() but immediately
releases the lock without holding a reference to the socket. A concurrent
close() can free the socket between the lock release and the subsequent
sk->sk_state access, resulting in a use-after-free.
Other functions in the same file (sco_sock_timeout(), sco_conn_del())
correctly use sco_sock_hold() to safely hold a reference under the lock.
Fix by using sco_sock_hold() to take a reference before releasing the
lock, and adding sock_put() on all exit paths.
CVSS Score
8.8
EPSS Score
0.0
Published
2026-04-06
In the Linux kernel, the following vulnerability has been resolved:
nfsd: fix heap overflow in NFSv4.0 LOCK replay cache
The NFSv4.0 replay cache uses a fixed 112-byte inline buffer
(rp_ibuf[NFSD4_REPLAY_ISIZE]) to store encoded operation responses.
This size was calculated based on OPEN responses and does not account
for LOCK denied responses, which include the conflicting lock owner as
a variable-length field up to 1024 bytes (NFS4_OPAQUE_LIMIT).
When a LOCK operation is denied due to a conflict with an existing lock
that has a large owner, nfsd4_encode_operation() copies the full encoded
response into the undersized replay buffer via read_bytes_from_xdr_buf()
with no bounds check. This results in a slab-out-of-bounds write of up
to 944 bytes past the end of the buffer, corrupting adjacent heap memory.
This can be triggered remotely by an unauthenticated attacker with two
cooperating NFSv4.0 clients: one sets a lock with a large owner string,
then the other requests a conflicting lock to provoke the denial.
We could fix this by increasing NFSD4_REPLAY_ISIZE to allow for a full
opaque, but that would increase the size of every stateowner, when most
lockowners are not that large.
Instead, fix this by checking the encoded response length against
NFSD4_REPLAY_ISIZE before copying into the replay buffer. If the
response is too large, set rp_buflen to 0 to skip caching the replay
payload. The status is still cached, and the client already received the
correct response on the original request.
CVSS Score
9.8
EPSS Score
0.002
Published
2026-04-03
In the Linux kernel, the following vulnerability has been resolved:
sunrpc: fix cache_request leak in cache_release
When a reader's file descriptor is closed while in the middle of reading
a cache_request (rp->offset != 0), cache_release() decrements the
request's readers count but never checks whether it should free the
request.
In cache_read(), when readers drops to 0 and CACHE_PENDING is clear, the
cache_request is removed from the queue and freed along with its buffer
and cache_head reference. cache_release() lacks this cleanup.
The only other path that frees requests with readers == 0 is
cache_dequeue(), but it runs only when CACHE_PENDING transitions from
set to clear. If that transition already happened while readers was
still non-zero, cache_dequeue() will have skipped the request, and no
subsequent call will clean it up.
Add the same cleanup logic from cache_read() to cache_release(): after
decrementing readers, check if it reached 0 with CACHE_PENDING clear,
and if so, dequeue and free the cache_request.
CVSS Score
5.5
EPSS Score
0.0
Published
2026-04-03
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: L2CAP: Validate L2CAP_INFO_RSP payload length before access
l2cap_information_rsp() checks that cmd_len covers the fixed
l2cap_info_rsp header (type + result, 4 bytes) but then reads
rsp->data without verifying that the payload is present:
- L2CAP_IT_FEAT_MASK calls get_unaligned_le32(rsp->data), which reads
4 bytes past the header (needs cmd_len >= 8).
- L2CAP_IT_FIXED_CHAN reads rsp->data[0], 1 byte past the header
(needs cmd_len >= 5).
A truncated L2CAP_INFO_RSP with result == L2CAP_IR_SUCCESS triggers an
out-of-bounds read of adjacent skb data.
Guard each data access with the required payload length check. If the
payload is too short, skip the read and let the state machine complete
with safe defaults (feat_mask and remote_fixed_chan remain zero from
kzalloc), so the info timer cleanup and l2cap_conn_start() still run
and the connection is not stalled.
CVSS Score
8.1
EPSS Score
0.0
Published
2026-04-03
In the Linux kernel, the following vulnerability has been resolved:
mtd: Avoid boot crash in RedBoot partition table parser
Given CONFIG_FORTIFY_SOURCE=y and a recent compiler,
commit 439a1bcac648 ("fortify: Use __builtin_dynamic_object_size() when
available") produces the warning below and an oops.
Searching for RedBoot partition table in 50000000.flash at offset 0x7e0000
------------[ cut here ]------------
WARNING: lib/string_helpers.c:1035 at 0xc029e04c, CPU#0: swapper/0/1
memcmp: detected buffer overflow: 15 byte read of buffer size 14
Modules linked in:
CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.19.0 #1 NONE
As Kees said, "'names' is pointing to the final 'namelen' many bytes
of the allocation ... 'namelen' could be basically any length at all.
This fortify warning looks legit to me -- this code used to be reading
beyond the end of the allocation."
Since the size of the dynamic allocation is calculated with strlen()
we can use strcmp() instead of memcmp() and remain within bounds.
CVSS Score
5.5
EPSS Score
0.0
Published
2026-04-03
In the Linux kernel, the following vulnerability has been resolved:
serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN
uart_write_room() and uart_write() behave inconsistently when
xmit_buf is NULL (which happens for PORT_UNKNOWN ports that were
never properly initialized):
- uart_write_room() returns kfifo_avail() which can be > 0
- uart_write() checks xmit_buf and returns 0 if NULL
This inconsistency causes an infinite loop in drivers that rely on
tty_write_room() to determine if they can write:
while (tty_write_room(tty) > 0) {
written = tty->ops->write(...);
// written is always 0, loop never exits
}
For example, caif_serial's handle_tx() enters an infinite loop when
used with PORT_UNKNOWN serial ports, causing system hangs.
Fix by making uart_write_room() also check xmit_buf and return 0 if
it's NULL, consistent with uart_write().
Reproducer: https://gist.github.com/mrpre/d9a694cc0e19828ee3bc3b37983fde13
CVSS Score
5.5
EPSS Score
0.0
Published
2026-04-03